Paper-qa

* Added more flexible typing, exported more types, added back reader default args

Fixed pickling bug about missing attribute and updated README

- Changed variable naming to be much more clear
- More types to avoid ambiguous dictionary/tuples
- Switched to using pydantic instead of dataclasses
- Removed non-core focus elements (caching, token counting, agents)
- Removed need to have texts/doc names in Docs, removing RAM problems
- Abstracted FAISS away, so any vector store can be used
- Removed ambiguous chunk/overlap defaults
- Added typewriter example to README
- Added caching example to README
- Made prompting more general
- Added unit tests for new name_in_text function
- Can pass by FileObj|Path|URL in add - (maybe add_path, add_file, add_url)
- Reduce code duplication in unit tests

Fixed bug in `add_text` not adding to Docs if an existing store is present

v.2.1.0
* Added dockeys to contexts
* Now we check hash on both `add_text` and `add`

* Made key_filters part of Answer object

* Added hash to document previews