Amend documentation to reflect parameter name change (#39)

Minor changes left out from PR #38 
Modifies documenting comments within `urlbuilder.py` and `urlhelper.py` to reflect the parameter name change.

imgix/urlbuilder.py

@@ -34,6 +34,8 @@ class UrlBuilder(object):
         `SHARD_STRATEGY_CYCLE`, domain sharding performed by sequentially
         cycling through the domains list.  (default `SHARD_STRATEGY_CRC`)
     sign_with_library_version : bool
+        Deprecated and to be removed in next major version
+    include_library_param : bool
         If `True`, each created URL is suffixed with 'ixlib' parameter
         indicating the library used for generating the URLs. (default `True`)