Add iOS7/iOS8 results for ES6
Add Array.prototype.contains to ES7 table.
Updated WebKit and IE results

WebKit now supports the ES6 Number constants and some String methods.

This also closes #245.
Merge pull request #254 from ziyunfei/Array#contains

Add Array.prototype.contains to ES7 table.
Merge pull request #255 from webbedspace/webkit

Updated WebKit and IE results
Implemented browser results interpolation

Now, if a result from a browser's version is not different from that of
its previous version, the result need not be recorded in the data files.
Instead, build.js will copy the result over automatically.
I've thus cleared out all unnecessary lines from data-es6.js. This has
resulted in a large diff, but you may observe the es6/index.html diff to
see that little has changed w/r/t the output results.

Note: browsers are determined to be the same version by comparing their
"full" string. As a result, certain older Chrome versions now have the
"full" string "Chrome, Opera", even though they predate Opera 15.

ALSO:
* Fixed a few Chrome and Firefox results as per #239.
* Fixed some older Firefox results that referenced "firefox28" instead
of "firefox27" (which comprises both 27 and 28).