Merge pull request #774 from ryanve/master

optimize _.mixin and _.wrap
Adding an 'Edge Version' link to the homepage
Merge branch 'master' of github.com:documentcloud/underscore
Fixes #771 -- removes custom toArray support and adds array-like support.
Fixes #740 -- debounced functions now return their last updated value
Fixes #738 -- makes sortBy a stable sort.
revising #738 -- implementation of stable sortBy
trying out the new CONTRIBUTING feature
tweaks to CONTRIBUTING
Clean up groupBy/countBy/sortBy.

* Remove superfluous argument to `lookupIterator`.
* Add context argument to `groupBy`, `countBy`.
* Streamline `sortBy`.
Merge pull request #780 from braddunbar/cleanup

Clean up groupBy/countBy/sortBy.
Fixes #648 -- adds  to Underscore.
Merge branch 'master' of github.com:documentcloud/underscore
Fixes #689 -- allow _.random() to be called with just a max, and use it in _.shuffle
Fixes #725 -- wording in the documentation of sortedIndex.
Fix #779 - Delimiters are used without escaping.
Use `slice` instead of non-standard `substr`.
Merge pull request #782 from braddunbar/delimiters

Fix #779 - Delimiters are used without escaping.
Fixes #729 -- reduceRight passes correct arguments for non-arrays.
Fixes #733  -- quick-fix implementation of isEqual on naked objects from different frames.