Moving towards 1.0
Added support for custom User models.

Note: get_username() is available since Django 1.5, however we're
going to drop 1.4 compatibility with django-envelope 1.0 anyway.
Removed Django 1.4 envs from tox.ini.
Mentioned dropping 1.4 support in changelog.
Be more DRY about version number in the docs.
Mentioned custom User model support in changelog.
Removed categorized ContactForm class.
Renamed BaseContactForm to ContactForm.
Updated form tests.
Removed unused settings.
Removed documentation for ENVELOPE_CONTACT_CHOICES.
Backwards incompatible changes section in the changelog.
Added initial cookbook with CategorizedContactForm.
Documentation cleanup.
Removed category from email_body.txt
Subject field is now optional.
Updated tests for optional subject field.
More meaningful test assertions (Python 2.7+).
Note about subject field in changelog.
Added supported Python versions to changelog.