Restored exponential quintessence in master branch
added python script to plot background
Merge branch 'albrecht_skordis' of https://github.com/miguelzuma/class_scf

Conflicts:
	plot_script_expquint.py
	source/background.c
Merge branch 'albrecht_skordis' of https://github.com/miguelzuma/class_scf

Conflicts:
	.gitignore
	source/background.c