added ability to plot PSFEx base functions
	modified:   psfex_demo.py
	new file:   psfex_demo_base_function_0.png
	new file:   psfex_demo_base_function_1.png
	new file:   psfex_demo_base_function_2.png
	new file:   psfex_demo_base_function_3.png
	new file:   psfex_demo_base_function_4.png
	new file:   psfex_demo_base_function_5.png