Renaming sourmash_lib module to sourmash

[luizirber]

The sourmash_lib name seems to come from the project early days, when the entry point was the sourmash 'executable' in the project root (for dev purposes).

If we use python setup.py develop we don't need the 'executable', and then we can use the name instead of sourmash_lib

[ctb]

-0 on this, at least for the way I work; I like to reference the sourmash script directly while I'm working on pythonland stuff, and having to run 'make' or 'python setup.py develop' seems like an added inconvenience.

[luizirber]

you already have to run python setup.py build_ext -i for it to work; python setup.py develop just need to be run once (during initial setup), if you are working on pythonland.

[ctb]

I've been thinking about this for a while and (serendipitously) came across this:

https://pip.pypa.io/en/stable/reference/pip_install/#editable-installs

and this:

https://setuptools.readthedocs.io/en/latest/setuptools.html#development-mode

which I didn't really understand before :). I will try it out and see what happens.

Is there a simple way to support both import sourmash_lib and import sourmash for the near future? The select_ksize debacle wrt load_signature was unpleasantly time wasting...