Pyctr

* Fix `setup.py` not including subpackages

* Document more classes, methods, and attributes
* Add a `pyctr.crypto.seeddb` module for central SeedDB management
* Loading SeedDB in `NCCHReader` is now removed
* Add new `TypeReaderBase` and `TypeReaderCryptoBase` for reader types that use a single file
* Fix `PathLike` error in `NCCHReader` and `RomFSReader`
* Changed type of `partition_id` and `program_id` in `NCCHReader` to `str`
* Some other changes. I'll get better at documenting this!

* Remove debug print in `SDFilesystem.open`

* Add the module `pyctr.type.sd` with the class `SDFilesystem`
* Add docstrings to `pyctr.crypto`
* Allow `os.PathLike`, `str`, and `bytes` as file paths in most methods
* Allow Windows-style paths in `CryptoEngine.sd_path_to_iv`

Initial standalone release. All previous commits are in the [ninfs](https://github.com/ihaveamac/ninfs) repo.