Add some sort of batch-test for the extensions that use the library

[LaCuneta]

While making a change needed for the Simple R Extension, I realized it would also affect the Python and JavaScript extensions as well. I tested Python with the change manually, but it occurred to me that it'd be nice to have some sort of subproject here (or elsewhere) that pulled in the known users of the library to test out any changes across them automatically so we don't miss any accidental breakage.