Appcli

Feature
* Use `Getter` classes to pick values ([`aa18b52`](https://github.com/kalekundert/appcli/commit/aa18b525339048603d0f7d75b93add1b020b1232))

Feature
* Add `SelfConfig` ([`39e3f3b`](https://github.com/kalekundert/appcli/commit/39e3f3b6126e93892f005d66121143adb570ede8))
* Make it easier to compose cast functions ([`2ef93e2`](https://github.com/kalekundert/appcli/commit/2ef93e2899921bfa25bea0ccf76fe40b88cefad4))
* Force layer values to be collections ([`dd82715`](https://github.com/kalekundert/appcli/commit/dd827158a7d69b28ca2bfbc95b493a1d79845d2d))

Feature
* Make key names optional ([`3a50d13`](https://github.com/kalekundert/appcli/commit/3a50d13c0c32966dfb22155f3caba58a30da992d))
* Allow subkeys to be specified using tuples ([`ac970dc`](https://github.com/kalekundert/appcli/commit/ac970dc6d6587f0b294596d8b84cb92f60540011))
* Teach FileConfig to read paths from attributes ([`328544c`](https://github.com/kalekundert/appcli/commit/328544cdfac14d19455dcc4cb3b0f11499adceb9))

Fix
* Respect default cast argument when using Key() ([`0442d69`](https://github.com/kalekundert/appcli/commit/0442d6954ae86a58a0e4371f28ab48f5db3c1207))

Feature
* Add an environment variable config ([`3c89019`](https://github.com/kalekundert/appcli/commit/3c89019d316727aecff319d982e6c012eca1ce8f))

Feature
* Allow parameters to control config order ([`12b8656`](https://github.com/kalekundert/appcli/commit/12b86563ebed29644533fd7ee895ae955bb26e87))
* Add convenience methods to load/reload app objects ([`f07de2b`](https://github.com/kalekundert/appcli/commit/f07de2b10fa88679535cd737fb4ea335dafb0268))
* Improve error reporting for mako templates ([`853f8b9`](https://github.com/kalekundert/appcli/commit/853f8b95f6345d9074cca820d4ea246a43f3f008))