SharedArrayBuffer and Atomics tests (#839)

INTERPRETING.md

harness/atomicsHelper.js

harness/testAtomics.js

...yBuffer/prototype/byteLength/this-is-sharedarraybuffer.js

.../ArrayBuffer/prototype/slice/this-is-sharedarraybuffer.js

test/built-ins/Atomics/Symbol.toStringTag.js

test/built-ins/Atomics/add/bad-range.js

test/built-ins/Atomics/add/descriptor.js

test/built-ins/Atomics/add/good-views.js

test/built-ins/Atomics/add/length.js

test/built-ins/Atomics/add/name.js

test/built-ins/Atomics/add/non-views.js

test/built-ins/Atomics/add/nonshared-int-views.js

test/built-ins/Atomics/add/shared-nonint-views.js

test/built-ins/Atomics/and/bad-range.js

test/built-ins/Atomics/and/descriptor.js

test/built-ins/Atomics/and/good-views.js

test/built-ins/Atomics/and/length.js

test/built-ins/Atomics/and/name.js

test/built-ins/Atomics/and/non-views.js