Byoc

Feature
* Add support for mutable default values ([`88894b6`](https://github.com/kalekundert/appcli/commit/88894b698b0cf40f01d591d51175961b20518b39))
* Make `inherited_param` compatible with all param subclasses ([`c65272f`](https://github.com/kalekundert/appcli/commit/c65272fd803e39607ef60d37b1f1161331431a1a))
* Implement `inherited_param` ([`518e80c`](https://github.com/kalekundert/appcli/commit/518e80c5012ce55af6de37d83e2d97c143b01163))

Fix
* Correctly handle unspecified docopt flags ([`30328c5`](https://github.com/kalekundert/appcli/commit/30328c51157a581b6d5291cbc20cf4fc23cb8b06))

Documentation
* Outline the README file ([`e3cd57d`](https://github.com/kalekundert/appcli/commit/e3cd57d78936749c113fe0e66a70cfb57896589c))

Feature
* Treat cast=... as a default when a key list is given ([`4567ad5`](https://github.com/kalekundert/appcli/commit/4567ad5236143e7b9299aeeebe408be6687aacbd))

Feature
* Use mako to render docopt usage text ([`9780f98`](https://github.com/kalekundert/appcli/commit/9780f98449fbbca0d0ed8b42aefa57f4d7feb019))

Feature
* Allows keys to be arbitrary callables ([`87a0b9c`](https://github.com/kalekundert/appcli/commit/87a0b9ce73a08c816109bbbce522811ef8655cf0))

Feature
* Add an easy way to toggle boolean parameters ([`ea7ba89`](https://github.com/kalekundert/appcli/commit/ea7ba8980848a0f6c46f2d0f293769ff76490ad3))
* Add a metaclass for circumventing the constructor ([`3120f36`](https://github.com/kalekundert/appcli/commit/3120f3617ac3dad668e788ecc7ac2ca75e1cd136))
* Add callback for when parameter value is changed ([`3a37468`](https://github.com/kalekundert/appcli/commit/3a37468ac729e6d202c32059030a299bb386945d))

Feature
* Add callback for parameter access ([`7c3bcf5`](https://github.com/kalekundert/appcli/commit/7c3bcf50164b6cc8633cc39037d626abd8b724df))