Added 2 extra let tests

These tests check for the temporal dead zone, and correct for-loop
iteration bindings. They are distinct from the basic let-test, as they
represent more advanced or nuanced functionality.
Altered the TDZ test to include const

Both const and let are subject to the temporal dead zone.
Fixed a small bug

Also updated IE11 support for for-loop iteration scope.
Const test now checks that assignment is an error

Assigning to a const should be a syntax error. This commit does not
update the test results to match this stricter test, yet.

This also fixes tabs introduced in previous commits.
Updating const results

Almost everything fails this updated test by treating const reassignment
as a silent failure instead of a syntax error.
Updated TDZ test results

Also fixed a bug in the Node test script.
Fixed Traceur result for the let-for test

Also made the test's code less wide.
Added explanatory notes about let/const support
Added an anti-hoisting check to the const test

I was previously hesitant to include this, but since most platforms'
const support is invalidated already by their lack of error-throwing,
adding this check doesn't disturb the results at all.
Implemented partial test results.

Now, tests in data-es6 can have, in place of a single test function, a number of sub-tests that check specific aspects of the feature. The let/const tests are the first features to be given this treatment.

Test result data in sub-tests is differential: if a browser is missing, the result for the previous version is used instead (with version lineage inferred from comparing the full names of the browsers).

This also redoes some of the CSS along with adding the styles necessary for partial test rows.
Fixed minor bug with colSpan setting
Added partial arrow tests
Implemented supertest drop-down button.

Subtests are now hidden by default, and must be revealed by clicking the button.
Added partial tests for default parameters.
Added partial tests for the spread operator.

This joins the previous 3 tests (spread call, spread array, spread string) into a single supertest.
Added partial tests for the class keyword

Also fixed some minor bugs in build.js.
Added partial tests for Typed Arrays. Closes #246.
Added partial tests for destructuring
Added partial tests for well-known symbols
Added partial tests for RegExp.prototype methods