* Mostly done.
* With all features enabled, it at least compiles.
* Fixed some bugs.
* Being explicit about degree type.
* More tests passing.
* Even more tests passing.
* Restoring optional Halo2 compilation.
* Fixing bad merge.
* Fixing lint errors.
* More lint fixes.
* Split of the backend implementations into trait categories.
* Some renamings.
* Much better function names.
* Removed option from witness.
* Pleasing the lint.
* Returning the proof.
* Removing filesystem stuff from backend.
* Renaming function.
* Another function rename.
---------
Co-authored-by: Leo <me@leoa.lt>