Add function to load boolean values from config

Improve installation instructions in README

Add conditional to account for different OpenGL header path on macOS.

If DARWIN is true OPENGL and GLUT variables contain links against the appropriate frameworks for macOS.

Conditional name DARWIN checks if you are compiling on a macOS/OSX system.

Smaller modification of pull request #24 - compiling issues on OSX

Change needed for compilation with gcc-6

On OS X the file system usually is case-insensitive, hence installing this script will overide the executable `music`.

-Wl,-z,defs is not supported on OS X

defs
Disallows undefined symbols in object files. Undefined symbols in shared libraries are still allowed.

removing it will not hamper performance of music

Python 3 Port

Fixed wrong conversion from pickled bytearray to str in MessageCallback. The pickle protocol adds some meta information bytes in front of the actual string, so a conversion to Cython str is invalid in general.

Missing virtual destructors.

Modified the .travis .yml file : modified the download location of get-pip, using minimal image of trusty, installing python-all-dev

Add a check for mpi4py version during Cython compilation.

Version 2 of mpi4py has changed the name of a submodule from mpi_c to
libmpi. We need to check which one to use at compile time.