Light-the-torch

Two minor bug fixes:

- warn if no PyTorch distribution is found during `ltt install` (28)
- fix extraction logic if a PyTorch distribution is contained in an extra (29)

This release enables to install PyTorch wheels from all channels (stable, test, and nightly) instead of hard-coding the stable channel. (27)

- pin pip version to < 20.3 (23)

- add initial support for inter PyTorch compatibility (22 )

For this release the CLI was rewritten (16). Instead of one overloaded command, `ltt` now has the subcommands `install`, `extract`, and `find`. For details see the [README](https://github.com/pmeier/light-the-torch/blob/ddca55f51b763565a992b753b3afdbeec118e4ad/README.rst). Furthermore, the minor Python API is now documented (#18).

- include `py.typed` to comply with [PEP561](https://www.python.org/dev/peps/pep-0561) (#13)