Fix build for mingw and dll linking
Add appveyor for continuous integration on windows
Add project files for Visual Studio Community 2013

Taken from https://github.com/darrenkopp/sassc-win
Credits go to @darrenkopp and @am11
Fix prelexer alternatives for 7 and 8 arguments
Move some modulo handling logic from parser to prelexer
Merge pull request #747 from xzyfer/wip/cleanup-modulo-todos

Fix some recently introduced TODOs
Fix for source-map issues

https://github.com/sass/libsass/issues/720
Merge pull request #742 from mgreter/feature/build-dll-win-mingw

Feature/build dll win mingw
Merge pull request #749 from mgreter/fix/source-map-issues

Fix for source-map issues