Migrate from `mtl` to `transformers` library.
Fix `ghc` compilation flags.
Introduce configuration and custom tagger support.

Including default configurations for ctags/hasktags.
Add `cache clean` command.
Introduce hashing mechanism.

Which prevent generating tags when the dependency graph have not been update.
Exclude current project from dependencies.
Replace usage of `ErrorT` with `EitherT`.
Fix command line 'usage' message.
Release 0.0.1.3.