Glsl frontend (#50)

* Basic glsl support

* Miscellaneous fixes and vertex shader works

* Added rudimentary texture and sampler support

* Basic preprocessor

* Added preprocessor if macros

* Pass tests and handle floats correctly

* Fix preprocessor if wrong precedence ordering when using macros
Refractor for the glsl parser
Partial primary expression parser

* Fix all clippy errors

* Cleanup

* Rollback formatting changes in lib.rs