Resolve "Restructure prior module"

Closes #444 (closed)

setup.py

@@ -70,7 +70,7 @@ setup(name='bilby',
       author_email='paul.lasky@monash.edu',
       license="MIT",
       version=VERSION,
-      packages=['bilby', 'bilby.core', 'bilby.core.sampler',
+      packages=['bilby', 'bilby.core', 'bilby.core.prior', 'bilby.core.sampler',
                 'bilby.gw', 'bilby.gw.detector', 'bilby.gw.sampler',
                 'bilby.hyper', 'cli_bilby'],
       package_dir={'bilby': 'bilby', 'cli_bilby': 'cli_bilby'},