Convert Makefile to a bash script

I've converted the non working Makefile to a somewhat modular bash script.
It iterates on configurable python versions (2.6 and 2.7 for now, like the
old Makefile).

Eggs have been parametrized in an array variable for easy expansion.
Update README with correct information
Add a tunable target directory
Add the possibilty to specify packages on command line
Fix wrong pypi2rpm install
Fix typo
Merge pull request #1 from clementmartin/master

Convert the makefile to a working shell script