Fix tautological pattern in tests

In neglecting to assert the type of error thrown (or that any error was
thrown at all), these tests cannot fail. Refactor the tests to use the
`assert.throws` helper method, which takes these details into
consideration.

Add tests for Proxy

Use the more common array syntax for includes

Fix monkey yaml's handling of carriage return

monkeyYaml didn't split lines correctly leading to \r in resulting
values.

Fixes #295

Insert omitted `negative` tag

Remove `$FAIL` function

This test exercises an early error, so it should be declared with the
`negative` tag.

This function is equivalent to `$ERROR` (which is automatically included
in test environments). Remove the harness file that defines the
function, remove references to the file from test `includes` lists, and
update scripts to instead invoke the `$ERROR` function.

Fixed testing deletion of an environment object.

Remove remaining includes for `assert.js` helper

No need to include asserts.js

The previous description of the 11.4.1-4.a-5 test case implied that an environment object could not be deleted while inside a with. However, the actual test was to test whether the variable declaration could be deleted. The description has been updated to better reflect this.

Add tests for early errors in module syntax

for..of additions

Generator test should specify generators feature.

Test 11.4.1-4.a-5 states that it verifies that an environment object cannot be deleted. However, this was giving a false positive. It was actually testing where a "var" declaration on an environment object cannot be deleted (there are other tests for this). This test case fails on Chrome 43, Firefox 38 and Internet Explorer 11.

Introduce the `module` flag to unambiguously identify tests that are
intended to be interpreted as module code.

Update contribution guidelines