Add unit-test for libsass issue 683

https://github.com/sass/libsass/issues/683
Improves main unit-test for new parser capabilities
Merge pull request #154 from mgreter/feature/ie-property-parsing

Add unit-test for libsass issue 683
Add and activate specs for random()
Merge pull request #151 from xzyfer/wip/issue_657

Add and activate specs for random()
Add and activate specs for issue 652
Merge pull request #156 from xzyfer/feat/issue-652

Add and activate specs for issue 652
Activate specs for issue 672
Merge pull request #157 from xzyfer/feat/activate-672

Activate specs for issue 672
Add spec for new colors (rebeccapurple and transparent)

https://github.com/sass/libsass/issues/699
https://github.com/sass/libsass/issues/700