"clean-cython" target added to Makefile, for pure python mode
"clean-cython" target added to Makefile, for pure python mode

It removes the C files and stuff, so that you can run in pure-python mode.
(if you just do a "make clean" then you also lose the fortran stuff)
nickvandewiele/RMG-Py,comocheng/RMG-Py,enochd/RMG-Py,KEHANG/RMG-Py,nyee/RMG-Py,chatelak/RMG-Py,KEHANG/RMG-Py,comocheng/RMG-Py,faribas/RMG-Py,nyee/RMG-Py,nickvandewiele/RMG-Py,chatelak/RMG-Py,faribas/RMG-Py,enochd/RMG-Py,pierrelb/RMG-Py,pierrelb/RMG-Py