Chembl-downloader

This PR does several things:

1. Removes dependency on `bioversions` and just implements the code locally
2. Adds a CLI for generating a statistics table for all versions of ChEMBL
3. Add proper project skeleton (documentation, unit tests, code quality assurance, CI)
4. Improve SQLite loading in case you delete the compressed data

Notebooks

1. Adds notebook about drug indications
2. Adds notebook about mapping to ChEBI

This release adds two new functions:

1. `chembl_downloader.download_monomer_library` which gets this file https://ftp.ebi.ac.uk/pub/databases/chembl/ChEMBLdb/latest/chembl_30_monomer_library.xml for whatever version you specify
2. `chembl_downloader.get_monomer_library_root` which does the same as the downloader but also parses the XML for you

Thanks to iwatobipen and his [recent blog post](https://iwatobipen.wordpress.com/2022/03/19/build-peptide-from-monomer-library-from-chembl-rdkit-chembl-chemoinformatics/) for inspiring this.

New Functions

- `chembl_downloader.download_fps` downloads the pre-computed Morgan fingerprint file
- `chembl_downloader.download_chemreps` downloads the chembl-smiles-inchi-inchikey map
- `chembl_downloader.get_chemreps_df` builds on `chembl_downloader.download_chemreps` and loads them in a pandas dataframe

Misc

- Add `isort` to code quality checking
- Enable many functions with `return_version` to make a tuple with the version, which is useful if you're having it infer the latest version.

This release adds the `get_substructure_library()` for automating the generation of an RDKit [substructure library](https://www.rdkit.org/docs/cppapi/classRDKit_1_1SubstructLibrary.html) as described in Greg Landrum's RDKit blog post, [Some new features in the SubstructLibrary](https://greglandrum.github.io/rdkit-blog/tutorial/substructure/2021/12/20/substructlibrary-search-order.html). The following example shows how it can be used to accomplish some of the first tasks presented in the post:

python
from rdkit import Chem

import chembl_downloader

library = chembl_downloader.get_substructure_library()
query = Chem.MolFromSmarts('[O,N]=C-c:1:c:c:n:c:c:1')
matches = library.GetMatches(query)


**Full Changelog**: https://github.com/cthoyt/chembl-downloader/compare/v0.1.2...v0.1.3

- Add `get_assay_sql()` function

**Full Changelog**: https://github.com/cthoyt/chembl-downloader/compare/v0.1.1...v0.1.2

Add more top-level imports for `download_sdf()`, `download_sqlite()`, and `latest()`