Add CHANGELOG.

CHANGELOG.md

+Version 2.0
+-----------
+  - Twitter API 1.1 support.
+  - Basic Authentication deprecated.
+  - friends_timeline() removed.
+  - mentions() removed and replaced by mentions_timeline().
+  - retweeted_by_user() removed.
+  - retweeted_by_me() removed.
+  - retweeted_to_me() removed.
+  - retweeted_by_user() removed.
+  - friends() removed.
+  - followers() removed.
+  - enable_notifications() removed.
+  - disable_notifications() removed.
+  - exists_block() removed.
+  - lists() removed and replaced by lists_all().
+  - is_list_member() removed.
+  - show_list_member added.
+  - is_subscribed_list() removed.
+  - show_list_subscriber() added.
+  - trends_location() removed.
+  - nearby_places() removed.