Adding edge encoding utility

[jjustison]

If wanted, here is a utility function for remapping the species edges onto the gene edges after reading in the gene tree.

Some of the stuff I've been working on uses the edge mappings and these mappings are lost when reading/writing the gene trees.

Let me know if this seems useful but you want more tests, documentation, clarification, etc.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files with missing lines	Coverage Δ
src/utils.jl	100.00% <100.00%> (ø)

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[cecileane]

That looks like a very useful and even necessary utility indeed. Thank you so much! I will review asap.
My first high-level thoughts are:

1. The test would ideally use a gene tree read from file, not a gene tree simulated during the tests, to show the main reason why this function exists and also to have an input gene tree with the default (empty) internal attributes, especially those modified by the function.
2. Given how useful this function could be to others, it would be great to export it and to add a section or subsection or page showing it in the documentation manual.

[cecileane]

@jjustison : could you please place this pull request on a branch other than your main branch? that will make it possible for all developers here to make edits to your PR. No rush, as you know!

[jjustison]

I created a new branch called edge_encoding. I am not sure if the the proper git flow but I will close this PR and open one from that branch.