- Remove trailing white space
- Streamline documentation of test tags
- Do not reference obsolete tags
- Document `features` frontmatter tag
- Document `es6id` frontmatter tag
- Omit unnecessary detail about test262 website generation. This is not
  directly useful to potential test contributors. Implementation details
  like these can be taken for granted by that audience.
- Remove documentation on YAML syntax. Details on YAML may be helpful
  for some new contributors, but this document should not attempt to
  cover the topic (especially not from the description of a specific
  frontmatter entry). Replace with a link to a more comprehensive source
  as this will be more generally useful to those who need it (and less
  obtrusive for those who do not).
- Consolidate information on test helpers
- Document `assert` helpers
- Update instructions for asserting errors. Since the introduction of
  `assert.throws` in gh-22, the preferred means of expressing
  expectations regarding errors has changed. Update the CONTRIBUTING.md
  file to reflect the latest approach. Explain purpose of `throw
  NotEarlyError;` in example test.
- Re-order information on file names. The inconsistency in the project's
  file names should not go unmentioned, but neither should it not
  preceed instructions for the accepted approach to namine tests.
- More clearly document required frontmatter tags. Explicitly list
  `description` as a required frontmatter tag, implicitly identifying
  all other tags as optional.

Extend coverage for GeneratorPrototype methods

Additional tests with incorrect for-in context

Iteration restructuring

MOP operations on non-configurable arguments-object property

Increment/Decrement with property accessor expression

Assignment with left-hand side property accessor

`Promise` methods should not be enumerable

Promise methods should not be enumerable, per https://people.mozilla.org/~jorendorff/es6-draft.html#table-4

Implement tests according to the pattern defined by the existing tests
for `GeneratorPrototype#throw`.

- Add missing ".prototype" lookup in Array.prototype tests (Follow-up of #280)
- Add noStrict flag in global/S10.2.3_A2.2_*.js (implicit this-binding is part of the test)
- Provide correct this-binding in function/13.2-*.js
- Add missing assert.throws in "set-iterator-close-after-add-failure.js"

Assert the value of the properties and update the test frontmatter to
include the `Symbol.iterator` feature.

Define tests for intrinsic Iterators under the appropriate subdirectory
of `built-ins`.

Update contribution information

Test262 now accepts community contributions. Update the copy on the
website to reflect this.

As written, the test behavior and description do not match--the
`throw` invocation takes place while generator execution is paused
*within* the `finally` block (not following it).

Ensure that the test exercises the described behavior (and remove
extraneous invocation of method under test).

As written, the test behavior and description do not match--the `throw`
invocation takes place while generator execution is paused *within* the
`try..catch` statement (not following it).

Ensure that the test exercises the described behavior (and remove
extraneous invocation of method under test).

fix case sensitive filenames

S15.4.4.4_A4.1 length enumerable should be checked on Array.prototype.concat

The test checks Array.concat which is undefined; instead it should check Array.prototype.concat.

Add tests for IdentifierReference as property

From the ES6 specification:

> ## PropertyDefinition : IdentifierReference
>
> 1. Let propName be StringValue of IdentifierReference.
> 2. Let exprValue be the result of evaluating IdentifierReference.
> 3. ReturnIfAbrupt(exprValue).
> 4. Let propValue be GetValue(exprValue).
> 5. ReturnIfAbrupt(propValue).
> 6. Assert: enumerable is true.
> 7. Return CreateDataPropertyOrThrow(object, propName, propValue).

23.2 Set Objects

commit c56030aea7b3e43f46dbbc2b52859ca275cff226
Author: Rick Waldron <waldron.rick@gmail.com>
Date:   Thu Apr 30 15:17:44 2015 -0400

    Fix nits

commit 9b341022a9fd5a295ce85b630886dae10e10b653
Author: Rick Waldron <waldron.rick@gmail.com>
Date:   Tue Apr 28 13:52:04 2015 -0400

    Wrap expected construct failure in assert.throws

commit 9ef7e1c0499a99b15c64bb480dbfa41433cf9804
Author: Mike Pennisi <mike@mikepennisi.com>
Date:   Fri Apr 24 13:46:02 2015 -0400

    Introduce addition tests for the Set constructor

commit bd54cccf4a599c123fae5c97782f5562cd9da8a0
Author: Rick Waldron <waldron.rick@gmail.com>
Date:   Fri Apr 24 15:11:19 2015 -0400

    23.2 Set Objects, additions

commit 970e2ca95879161a8bb124ec712f7333fdea6798
Author: Rick Waldron <waldron.rick@gmail.com>
Date:   Tue Apr 21 12:44:41 2015 -0400

    23.2 Set Objects

The increment/decrement operator evaluates its operand expression once. When
the operand expression is a property accessor, RequireObjectCoercible
and ToPropertyKey are called on the property accessor in the correct order.

Enable strict mode for more built-in tests

Use a very negative number so ES5 implementations don't loop forever

Mapped arguments property is changed to non-configurable. Check
arguments mapping works correctly when applying various MOP
methods.

The assignment operator evaluates its operands from left to right. When
the left-hand side expression is a property accessor, RequireObjectCoercible
and ToPropertyKey are called on the property accessor before the right-hand
side expression is evaluated.

- Remove no longer needed noStrict flags.
- Change tests to use propertyHelper.js for strict mode compatibility.
- Add tests for return value of `delete` operator, e.g. `delete Array.prototype === false`.
- Add non-writable tests for global NaN property.
- Split some tests to run in strict mode.
- Change tests with global `var length` declaration to use a different variable name for browser environments.
- Merge duplicated tests symbol-data-property-configurable-non-strict and symbol-data-property-configurable-strict.
- Merge duplicated tests symbol-data-property-writable-non-strict and symbol-data-property-writable-strict.
- (And a small change in propertyHelper to reduce code duplication in function call.)

Add new tests for Math built-ins

S15.4.4.5_A3.1_T1.js: Fix inconsistent error message