Rename env vars

The user can now rename environment variables within the config class.

i.e.

# echo $APP_DEBUG
# "true"
config.from_envar("APP_DEBUG", rename="DEBUG")
assert config["DEBUG"] == True

Refactor Tailor class

Refactor the tailor class by removing the local store and utilizing native dict like functionality.

Fix KeyError bug

Fixes KeyError bug described in #11.

Fix bugs, add tests

Fixed some small bugs and added more tests.

First release!

This is the first release of pytailor.