Merge branch '245-proposal-library' into 'master'

bilby/core/prior.py

bilby/core/sampler/__init__.py

bilby/core/sampler/cpnest.py

bilby/core/sampler/proposal.py

bilby/gw/prior.py

bilby/gw/prior_files/GW150914.prior

bilby/gw/prior_files/aligned_spin_binary_black_holes.prior

bilby/gw/prior_files/binary_black_holes.prior

bilby/gw/prior_files/binary_neutron_stars.prior

bilby/gw/sampler/__init__.py

bilby/gw/sampler/proposal.py

examples/injection_examples/custom_proposal_example.py

test/gw_prior_test.py

test/prior_files/binary_black_holes.prior

test/prior_files/binary_neutron_stars.prior

test/prior_test.py

test/proposal_test.py

test/sampler_test.py