Refactor package names

Do a refactoring pass where we change package names (we need to do this in file names and `setup.py`). Currently, most packages contain `_new` in the name (which should be removed) and also they should be moved under pash_annotations (or annotations) in the directory, so that users can import them as `import pash_annotations.parser` instead of `import parser_new` (which could be a package from an arbitrary library that has nothing to do with PaSh).

Also, we should rename `main.py` to something like `annotation_cli` and also include it in the pip package (by adding it to `setup.py`).

@festutz could you take a stab at those changes in a PR that is targeted to main?