Added HIF functionality

[nwlandry]

This PR does the following:

• Adds the ability to create bipartite edgelists for directed hypergraphs
• Adds the ability to read and write HIF json files.

[codecov]

Codecov Report

Attention: Patch coverage is 14.51613% with 106 lines in your changes missing coverage. Please review.

Project coverage is 90.36%. Comparing base (4def3d4) to head (195de21).

Files	Patch %	Lines
xgi/readwrite/hif.py	10.00%	99 Missing ⚠️
xgi/convert/bipartite_edges.py	30.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #563      +/-   ##
==========================================
- Coverage   92.51%   90.36%   -2.15%     
==========================================
  Files          59       60       +1     
  Lines        4393     4513     +120     
==========================================
+ Hits         4064     4078      +14     
- Misses        329      435     +106     

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[nwlandry]

Closing this because it's stale, and because some of the functionality has been implemented in PR #354.