Find name not taken on pypi: pyrh

* Update README
* Update example.ipynb
* update pyproject.toml
  * include python2 requirements
* update poetry.lock
* Fix imports
* Remove setup.py

Merge pull request robinhood-unofficial#49 from dsouzarc/invalid_stoc…

…k_exception

Adds custom Exceptions + more consistent spacing + documentation

Merge pull request robinhood-unofficial#39 from josh-ua/master

Only get positions with shares you own in securities_owned