Mutwo.csound

This adds support for the new 'mutwo.core' version.

Added
- `mutwo.csound_converters.configurations.CSOUND_BINARY` to set path to csound binary

Changed
- modernized dependencies, testing structure

Fixed
- docstring

Changed
- to new `mutwo.core` version with parameter based duration model
- `mutwo.ext-csound` to `mutwo.csound`

Changed
- `EventToSoundFile` argument `csound_score_converter` to `event_to_csound_score`
- improved warnings

Changed
- `constants` to `configurations` and `constants`

Changed
- refactored `CsoundScoreConverter` to `EventToCsoundScore`
- refactored `CsoundConverter` to `EventToSoundFile`
- package structure to namespace package to apply refactor of mutwo main package