New first diffusion code.  Follows original plan, but is more readable now.
Updated .gitignore with the assumption that the MMSP for beginners document will be a permanent part of the distribution.  Needs updating to make it really useful.
Updates to 1st diffusion and manual.  Just the start.  A long way to go yet.
Included gnuplot functionality and tried to get to ANSI C++ standards.
Merge pull request #2 from lucentdan/master

New first diffusion code.