add program to calculation one-photon absorption spectrum
	modified:   .gitignore
	modified:   Makefile.am
	new file:   absorption.c
	new file:   absorption.h
	new file:   calc-theta.h
	modified:   coeffs-pert-other.c
	modified:   coeffs-pert.c
	new file:   integration.c
	new file:   integration.h
	modified:   matrix-element-pert.h
	new file:   onephoton.c
	modified:   saveV.c
	modified:   savem.c
	new file:   tensors.h
	modified:   three-vector.c
	modified:   three-vector.h