`zipfile.ZipFile` is typed to accept `Text` for local and archive file
paths. In Python 3.6, several `ZipFile` methods accept `pathlib.Path`
objects, not just `str` objects. Generalize `ZipFile`'s methods so code
using `pathlib.Path` with `ZipFile` type-checks.
I verified (using my own project) that the following methods work with
os.PurePath at runtime on CPython 3.6:
* zipfile.ZipInfo.__init__
* zipfile.ZipInfo.extractall
* zipfile.ZipInfo.write
- ThreadError exists (undocumented) on Python 3. It's an alias for _thread.error,
but making it a separate exception seems fine.
- zipfile.error is an alias for BadZipFile on both Python versions.
- zlib.Compress and Decompress are not actually accessible at runtime.
