Refactor Python module API to prefer methods over constructors

[jabraham17]

Refactors the Python module API to prefer methods over constructors. The old constructors are still available and still useful in some places, but for the most part users should prefer the new API.

Old style

var interp = new Interpreter();
var mod = new Module(interp, 'mod');
var func = new Function(mod, 'myfunc');

New style

var interp = new Interpreter();
var mod = interp.importModule('mod');
var func = mod.get('myfunc');

This PR also makes a few other changes

• renamed the internal .get to .getPyObject

• renamed getAttr/setAttr to get/set

• renamed getIdx/setIdx to get/set

• added support for passing kwargs to .call

• made a variety of doc cleanups/reordered code for better clarity

• st test/library/packages/Python

• st test/library/packages/Python with GASNet

[Reviewed by @lydia-duncan]

[lydia-duncan]

Nice! This looks like a great improvement. I have some comments inline, though most of them are minor

[lydia-duncan]

🎉

[jabraham17]

After fixing the docs build, I followed up with a few more doc improvement tweaks in 9dc61a9