v0.8.1 - Fix bug with creating pyarrow table with empty column

Trying to create a pyarrow table that has an empty (all zero-length) column of string values fails. This is because the underlying buffer is empty, and c++ just gives us a null pointer. Pyarrow validates that the buffer passed to the array creation functions is non-null.

This was fixed by allocating and saving a correctly aligned pointer to an empty buffer, and returning that in cases where we would try to use a null pointer.

PyArrow support & new CI workflow

Pytubes 0.8.0 brings support for creating PyArrow tables efficiently from tubes, allowing a method to generate pyarrow/pandas tables without python overheads

This release is being made using a new github actions workflow that provides binary wheels for multiple python versions on Linux, Windows, and OSX as well as deploying docs and artifacts automatically.