De-duplicate dependencies from PlanetaryCodeCollection

[sampotter]

Right now we have duplicated versions of C files from @nschorgh's PlanetaryCodeCollection in this repository, but eventually the ideal setup will be one of the following:

Option 1:

1. made PCC a submodule of this repository
2. clone PCC & compile
3. tell setup.py the location of the compiled static or shared libraries

Option 2:

1. clone and compile PCC
2. install static or shared libraries + headers system wide
3. tell setup.py to look for these libraries and headers

Then we won't have any duplicated code between the libraries and we can pull in changes that Norbert makes directly in the PCC repo.