include pure python and cpp modules

[lacava]

Right now the package seems to just pick up the pybind11 module. I would like to move this to a brush.core module, and have other submodules of brush that are pure python. example: https://stackoverflow.com/questions/47599162/pybind11-how-to-package-c-and-python-code-into-a-single-package#47651621

[lacava]

@JDRomano2 let's talk about this next meeting