New module: sourmash compare

[taylorreiter]

This PR adds a new multiqc module for the output of sourmash compare (#1805). It was modeled after the vcftools relatedness2 module. I left space for future sourmash modules that I will implement soon.

• This comment contains a description of changes (with reason)
• CHANGELOG.md has been updated

New module checklist:

• There is example tool output for tools in the https://github.com/ewels/MultiQC_TestData repository or attached to this PR
• Code is tested and works locally (including with --lint flag)
• docs/README.md is updated with link to below
• docs/modulename.md is created
• Everything that can be represented with a plot instead of a table is a plot
• Report sections have a description and help text (with self.add_section)
• There aren't any huge tables with > 6 columns (explain reasoning if so)
• Each table column has a different colour scale to its neighbour, which relates to the data (eg. if high numbers are bad, they're red)
• Module does not do any significant computational work

Test data:
This test data is two files, the *labels.txt file and the numpy array that is output alongside the labels.txt document. I've zipped them together to allow for upload to the PR, but they should be unzipped and uploaded as separate files to the https://github.com/ewels/MultiQC_TestData repository.
gut_compare.zip

[vladsavelyev]

Thank you for writing this module!

I made some refactoring, mainly:

• the extra compare2matrix felt like an unnecessary abstraction
• simplified parsing - data.tolist() is extactly the input heatmap.plot expects, so no need to go through an extra intermediate dict (and in the future, we should even be able to use numpy arrays directly without extra copying!)
• minor clean up and uncommenting self.write_data_file()

[ewels]

Couple of very small comments, but generally looks great and happy for this to be merged once those are addressed 👍🏻