Don't split a block with @at-root unless necessary.

Closes #1239
Merge remote-tracking branch 'origin/stable' into stable
Merge remote-tracking branch 'origin/stable' into stable
Updated Number Operations for Unit Math

See [multiplication error](https://github.com/nex3/sass/issues/83). This comes up all the time and the current documentation implies that Sass will do unit conversion for them for everything.
Fix a sass-convert comma-folding bug.

Closes #1257
Fix @media interpolation errors.

Closes #1260
Merge pull request #1261 from Snugug/stable

Updated Number Operations to include Unit Math
Merge remote-tracking branch 'origin/stable' into stable
Bump VERSION to 3.3.8.
Clarify that any value can be a legal key in a Sass map.
Clarify how colors work in the sass reference.
Fix markdown syntax mistake.
Disallow functions named "and", "or", or "not".

Closes #1265
Update Chris's bio.

:)
Add GHFM code fences to blocks
Fixed small documentation issue (in `@at-root`)

Fixes #1283
Fix deprecation warning File.exists? -> File.exist?
Update ruby patch version

https://www.ruby-lang.org/en/news/2014/05/09/ruby-2-1-2-is-released/
Stop skipping Ruby 2.1 on Travis.

The outstanding bug has been fixed as of 2.1.2.
Merge remote-tracking branch 'origin/stable' into stable