big binary file engines

[nvictus]

Description

What was changed in this pull request?

bigWig signal and bigBed coverage tiles can be served by either pybbi or pyBigWig. Default engine is to choose whichever one is installed ("auto").

Why is it necessary?

Having alternative backends in case one library is too difficult to install on a given system.

Checklist

• Unit tests added or updated
• Updated CHANGELOG.md

[pkerpedjiev]

Which library do you envision being installed by default?

I presume the default use case for this will be Jupyter. @mccalluc did some work moving some of the docs from the higlass repo to here so perhaps updating the section on bigWig under docs/genomic would be helpful?

[nvictus]

Which library do you envision being installed by default?

For now, let's keep bbi the default.

updating the section on bigWig under docs/genomic would be helpful

The docs for bigwigs describe ingesting via docker. I think choosing engines would be more relevant to the higlass-python/Jupyter docs.