We're not going to implement demo apps anymore!

Just run the parallel algorithm in main.
Also restructured the Makefile.
Rename `main` -> `mpi_convex_hull`.
Patch codebase to let it compile in Linux.

Specifically, `struct timezone` raises problems in Ubuntu 12.10. Plus, it is
needed to add `-lm` to the end of the compilation command to enable math
functions (in OS X 10.8 it works well with and without the flag).
Merge branch 'master' of github.com:stefanozanella/mpi_convex_hull