fixed lahman.py; added test_lahman.py

[mlinenweber]

• Fixed lahman.py - now downloads from dropbox [does so in a generic way, by finding the link in http://seanlahman.com]
• Added test_lahman.py
• Refactored conftest.py, by combining response_get_monkeypatch and bref_get_monkeypatch to use target_get_monkeypatch [they differed by only 1 line].
• Added fixtures get_data_file_bytes and target.
• Updated documentation.
• Updated setup.py to install py7zr and requests_cache

fixes #391

[bdilday]

there is also a fix here #434
I think there's a preference to avoid relying on 7-zip and py7zr?

[bdilday]

I meant this PR #435

[mlinenweber]

Respectfully, I don't know of any reason why not to use 7zip/py7z. Now, the justification to use it is that it is the compression format Sean Lahman has chosen. Furthermore, to that extent, I don't think it is appropriate to rely upon a third-party to host a zip file. (Same goes for putting the zip file into this repository). I would rather go directly to the source, i.e., seanlahman.com - that way when he updates the data this library can download the latest without delay.

Can discuss more here or on Discord. Thanks.