Develop: Improved usability of makefiles

Added a makefile to replace mastermake, which calls the lower level make
files.  This allows systems that cannot update their default compiler
to install davitpy without manually changing all of the lower level
model makefiles.

Lower level makefiles (iri, hwm, tsyganenko, and raydarn) and the
README were also updated to be compatible with this change.

Excess spaces were removed from MPIutils.f90 since I opened it to see
what it did.
The directories containing IGRF (https://github.com/vtsuperdarn/davitpy/tree/develop/models/igrf) and MSIS (https://github.com/vtsuperdarn/davitpy/tree/develop/models/msis) code do not contain any shared library objects. I don't think that they are pre-compiled but that instead they are compiled by the setup.py file when one executes `python setup.py install --user`. Do you see the same thing?