Implement negative '@for' loops (Fix #703)
Implement new colors (rebeccapurple and transparent)

Fix https://github.com/sass/libsass/issues/699
Fix https://github.com/sass/libsass/issues/700
Implement inspect function (Fix #701)

This also implements missing Map Inspect Operator!
Implement feature-exists()
Merge pull request #705 from mgreter/fix/negative-for-loop

Implement negative '@for' loops (Fix #703)
Merge pull request #706 from mgreter/feature/inspect-function

Implement inspect function (Fix #701)
Merge pull request #707 from mgreter/feature/new-colors

Implement new colors (rebeccapurple and transparent)
Merge pull request #709 from xzyfer/feat/feature-exists

Implement feature-exists()