Changes to make pygbe run.

 * Import lpmv from scipy.special instead of scipy.special._cephes.
 * Replace python2.6 with python2.7 in Makefiles.
 * Also clean .pyc files in bem_pycuda when make cleanall is called.
 * Update .gitignore.
Detect the version of python in the Makefiles.

 * Set up the include paths using this version.
Update the README file.

 * Use Markdown.
Add .md extension to README.