Mason modify bug fix + Mason Makefile update

[ben-albrecht]

This PR fixes 2 bugs:

1. Addresses an arg-parsing bug in mason add/rm
2. Ensures make mason always rebuilds if any mason source file is modified

Additionally, this PR refactors the masonModify() function body, and updates the masonModify tests to exercise the arg-parsing machinery, so that it would catch the bug fixed here.

Testing

• local: start_test test/mason

[oplambeck]

Looks good to me, passed a start test on my end. Couldn't break it or get unexpected behavior playing around with it

[Spartee]

I had some nit-picks but overall this is great. Im approving to leave it to you to decide to address nits or not.