Refactor
- harmonized terminology for arguments/parameters
- **types**: more descriptive ArgType creation from functions, documentation
BREAKING CHANGE
- The following classes have been renamed: BaseArg -> Arg, Cmd -> Expander, Arg -> Param, ArgType -> ParamType
- ArgType.from_function is renamed to ArgType.from_function_that_raises
Feat
- **types**: add case normalization in ArgType.choices[_str]
- **sources**: add support for generic command line flags