Fixes
- Fix segfault when comparing pseudo selectors (@xzyfer, #2289)
- Fix thread-safety for mixin recursions check (@mgreter, #2286)
- Fix false parser errors (@xzyfer, #2095)
- Fix bad source mappings for interpolated selectors (@mgreter, #2224)
- Fix not erring when encountering bad interpolations (@mgreter, #2081)
- Fix some error messages to match Ruby Sass (@mgreter, #2267)