Add missing `RankNTypes` extension and match `inlinable` names
Use `tasty` instead of `test-framework`

The tests are still broken. They need to be updated to lens based
parsing.
Return `Nothing` when end of input is reached in `parsed` and `parsedL`

Previously to distinguish between an end of input and a parsing error,
the message of decoding error had to be inspected.
Update tests for lens based parsing

The tests cover leftovers input pushback when unsuccessful parsing.
Use `parsedL` for `parsed` to avoid code duplication
Polish code

- Remove sample tests.
- Clean up imports.
- Remove unused GHC extensions.
- Extend documentation.