Adds more passing and failing tests

I’ve added most of the test I wrote when I tried to do something like this myself. You’ve done an awesome job, pretty much everything is covered already. Only the last four don’t pass:

- Indented comments aren’t supported
- Mixins with arguments get an extra semicolon
- Property nesting gets an extra semicolon
- Property syntax isn’t supported (probably the least important one, personally I’ve never seen anyone use it)