Merge pull request #26 from metajack/linux-gpu

Enable Skia GL on all platforms
Free context when draw target is freed.
Don't create extra reference to GL context on new.
Merge pull request #27 from metajack/mem-leak

Fix GL context leak.
Fix debug and release compiles.
Merge pull request #28 from metajack/debug-fixes

Fix debug and release compiles.
Update for language changes