Bumps version to 0.2.1.
Adds 0.2.1 changes to change log.
Release 0.2.1

* Reformats ``README.rst``.
* Renames change log file to ``*.rst``.
* Adds authors and contributing files.
* Sets up Travis CI.
* Adds version to ``__init__.py``.
* Fixes #5. Make ``accented_to_numbered()`` add apostrophes when needed.
* Fixes #4. Fixes ``numbered_to_accented()`` handling of ``'v'`` vowel.
* Fixes #3. Changes ``IndexError`` exception handlers to ``KeyError``.
* Fixes #2. Fixes ``accented_to_numbered()`` with uppercase accented vowel.