Chag

* Refactored to use classes and cleaned up implementation
* Added a ``new`` command used to create a ``Next Release`` entry.

Python 3 compatibility

Rewritten in Python using Click.

* Added the `append` command.
* Added the ability to get messages from an external editor.
* Added the ability to link Github issues and git commits.

Adding new commands and changing how parsing works.

* Made ``TAG`` a required argument for ``parse`` and ``tag``.
* ``parse`` now only outputs the contents of the changelog entry to STDOUT.
* Added ``list`` and ``latest`` commands.
* Added an ``update`` command that can be used to update a CHANGELOG TBD
heading with a new changelog entry.

* Using ``set -e``
* Simplifying function names and error handling.

* Using POSIX style regular expression to work with GNU grep.
* Added a ``--version`` option.
* Writing errors to STDERR.
* Added a bats test suite.