Use cPickle instead of pickle

Change Parso to use cPickle instead of pickle when reading/writing the
cache, which speeds up the cache significantly.

In Python 2, cPickle is up to 1000 times faster than pickle. (In Python
3, if you "import pickle", you are actually getting cPickle.)

As is the convention, the code tries to import cPickle, and if that
fails, it falls back to pickle.

This has a big impact for users of jedi-vim, since in many cases Vim
uses Python 2.

parso/cache.py

@@ -4,11 +4,15 @@ import sys
 import hashlib
 import gc
 import shutil
-import pickle
 import platform
 import errno
 import logging
 
+try:
+    import cPickle as pickle
+except:
+    import pickle
+
 from parso._compatibility import FileNotFoundError
 
 LOG = logging.getLogger(__name__)

parso/pgen2/grammar.py

@@ -16,7 +16,10 @@ fallback token code OP, but the parser needs the actual token code.
 
 """
 
-import pickle
+try:
+    import cPickle as pickle
+except:
+    import pickle
 
 
 class Grammar(object):