Created find_motifs_iter to iterate over results

[Raphtor]

Maintained find_motifs for backward compatibility.

[codecov-commenter]

Codecov Report

Merging #17 (d1d8770) into master (7ee70db) will increase coverage by 0.41%.
The diff coverage is 87.23%.

@@            Coverage Diff             @@
##           master      #17      +/-   ##
==========================================
+ Coverage   86.63%   87.05%   +0.41%     
==========================================
  Files           4        4              
  Lines         419      448      +29     
==========================================
+ Hits          363      390      +27     
- Misses         56       58       +2     

Impacted Files	Coverage Δ
grandiso/__init__.py	85.71% <75.00%> (-0.62%)	⬇️
grandiso/test_grandiso.py	100.00% <100.00%> (ø)

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[j6k4m8]

This is awesome, and it's going to get us a huge performance bump in a few current bottlenecks!

I pushed two commits to the tail end which:

• Add type annotations for the generator
• Add some basic tests for the find_motifs_iter call
• Add this update (with credit! woo) to the changelog

Take a look and make sure I made everything in the spirit of your PR, and then let's merge!