Cross-Platform Compatibility and PyBurn

This release replaces the postprocessor with one written entirely in Python and Fortran, which adds functionality and support for additional output formats, and eliminates complicated library dependencies. ExoPlaSim is also now confirmed to run on Mac OS X Catalina, Windows Subsystem for Linux, Ubuntu and CentOS, and with GNU C/Fortran compilers ranging from gcc4 to gcc10. X11 dependency has also been removed.