so that:

- `python -m coglet` is the main entrypoint
- `cog` compatibility imports are a thin wrapper around `coglet.api` and
  are only available for import once `coglet/_compat` is put into
`sys.path`, thus greatly reducing the likelihood of import collisions.
- `cog/internal/` directory collapsed up a level to `coglet/` since the
  above import collision problem is fixed.

and rename test func to not shadow submodule name.