Added pastro

changes:

• renamed bin/postscripts/plot_intrinsic_posterior.py → bin/postscripts/compute_posterior.py
• reorganized jacobians from bin/postscripts/plot_intrinsic_posterior.py to src/rapidpe_rift_pipe/jacobians.py
• src/rapidpe_rift_pipe/pastro.py contains all utility functions for pastro calculations
• compute_evidence in src/rapidpe_rift_pipe/postscript_utils.py computes evidence for pastro calculation