Fix pickle

Saving as pickle was failing for me because the extension was still unknown to parts of the code.

I fixed some documentation and removed the unused gzip argument from Result.__init__

We should add some tests as well before we merge this in.

bilby/core/result.py

@@ -43,6 +43,8 @@ def result_file_name(outdir, label, extension='json', gzip=False):
     =======
     str: File name of the output file
     """
+    if extension == 'pickle':
+        extension = 'pkl'
     if extension in ['json', 'hdf5', 'pkl']:
         if extension == 'json' and gzip:
             return os.path.join(outdir, '{}_result.{}.gz'.format(label, extension))
@@ -735,7 +737,7 @@ class Result(object):
             default=False
         outdir: str, optional
             Path to the outdir. Default is the one stored in the result object.
-        extension: str, optional {json, hdf5, pickle, True}
+        extension: str, optional {json, hdf5, pkl, pickle, True}
             Determines the method to use to store the data (if True defaults
             to json)
         gzip: bool, optional