Merge branch 'master' into potential

* master:
  added python script to plot background
  Restored exponential quintessence in master branch
Merge branch 'potential'

* potential:

the potential has been restored to the (more general) Albrecht-Skordis type. The last commits have been just a consequence of not understanding some details of git, and can be safely ignored
n-th attempt to re-implement the AS potential in master.
Merge branch 'AS_pot'

* AS_pot:
  n-th attempt to re-implement the AS potential in master.
this is not working!!!
Conflicts:
	source/background.c
trying (hard) to merge the old potential