Generalizing point base features, a few other fixes

[bpben]

Main thing trying to do here - enable a config to specify that there are multiple point-based features in one file (rather than repeating the information again for each feature).

There are also some documentation updates here, part of ongoing process

Also - noticed a major issue with how crashes were being joined to segments related to segment_ids being mixed types. Should now be fixed.

[codecov-commenter]

Codecov Report

Merging #318 (ca49f8f) into master (bf9267e) will increase coverage by 0.40%.
The diff coverage is 88.04%.

@@            Coverage Diff             @@
##           master     #318      +/-   ##
==========================================
+ Coverage   64.02%   64.42%   +0.40%     
==========================================
  Files          33       33              
  Lines        3263     3314      +51     
==========================================
+ Hits         2089     2135      +46     
- Misses       1174     1179       +5     

[j-t-t]

Boston, philly, dc and chicago configs use point based features. Do these configs need to be updated, or is the formatting still the same?

Did you use this to add any features to any city?

Can you add a test for create_segment that shows adding multiple features in one file?

Also looks like something's going on with the pinned mac version

[j-t-t]

indentation here also looks weird

[bpben]

Huh, this one seems fine to me? Indent within brackets?

[bpben]

Thanks for the comments, needed actually do some more edits, handling categorical variables a bit differently, requiring less preprocessing. Added docs.

Also - this should still work fine for old configs, it will just process them differently if they have multiple features per additional source. README has deets.

[bpben]

@j-t-t also, do you think the test in create_segments is necessary? I have the test for multi feature in standardize_points:

crash-model/src/data_standardization/tests/test_standardize_point_data.py

Line 154 in 052761a

def test_read_file_info_multi(tmpdir):