Mark obsolete engine versions in ES6 compat table.

All engine versions that are no longer officially maintained (at time
of commit) are marked as obsolete in the ES6 compatibility table. When
an engine is marked as obsolete, the "obsolete" class is added to each
respective table cell when building the output HTML file.
Auto-hide obsolete engines in ES6 compat table.

Result table cells (and thus columns) of obsolete browsers are hidden
via CSS. A checkbox allows for showing the hidden data.
Re-Add Firefox 28 results from #87.

Pull Request #87 did only change the (generated) index.html. This commit
adds the results to the data-es6.js and includes the generated file.
Merge pull request #88 from fbender/es6-ux3

Usability enhancements, Part 1, 2nd try (issue #75)
Unify mechanism for showing obsolete browsers. Some styling tweaks.
Update Node results to 0.11.7
Fix for test with multiple scripts

Previous version was always failing tests for let statement and generator functions. The reason for this was the fact, that `eval('if (false) { true }')` returns `undefined`, which was causing failing tests.
Merge pull request #90 from pepkin88/patch-3

Fix for test with multiple scripts
Update Node Harmony results
Update Node Harmony results
Merge pull request #91 from pepkin88/patch-1

Update Node Harmony results after fix #90
Highlight rows/columns
Add support for "showing" only 1 column