support github vs. python product capitalization differences

[sbailey]

This PR fixes #172 by supporting installing products where the github name has a different capitalization than the python package name, e.g. https://github.com/desihub/QuasarNP hosting quasarnp. Tested with

desiInstall -v -r $SCRATCH/desi/test QuasarNP 0.1.0

(that outputs to NERSC /global/cscratch1/sd/sjbailey/desi/test, but I suggest running it yourself for testing...)

[weaverba137]

Perhaps I caught this PR in a preliminary stage, but there's a lot left to do here.

[weaverba137]

As I mentioned in #172, these are not the only possible combinations. This change also needs to be applied to the case where the package lives in a py/ directory. Finally, we need unit tests for all of these cases.

[sbailey]

I expanded a unit test for the new case where the product name is Capitalized by the python package isn't, e.g. QuasarNP/quasarnp, so these two cases are now supported and tested:

• capitalization of the product and the python package agree (most of our products)
• the product is Capitalized but the python package in the top level directory is all lowercase (e.g. QuasarNP/quasarnp)

However, I'm going to push back about adding support for these additional cases:

• python package under py/ whose capitalization doesn't match the GitHub product name
• GitHub product and python package having different capitalizations but the python package isn't entirely lower case

We don't have any cases that match either of those right now, and I don't anticipate having those cases in the future. I suggest that this PR adds new needed functionality without breaking old functionality, even if it doesn't additionally support all possible pathological future cases.

[weaverba137]

OK, I see your point. I will merge and tag soon.