Beet

Feature
* Plugin "project_advancement" ([`160ec91`](https://github.com/mcbeet/beet/commit/160ec918ab1a600742a19ddb8b09ae23fd81265c))

Fix
* Coerce plugin options to concrete types ([`dd2de5a`](https://github.com/mcbeet/beet/commit/dd2de5a10c01f8e8dd6ef59072879751c3f7a3e8))

Feature
* Add configurable decorator to load and validate plugin options ([`a3a39fe`](https://github.com/mcbeet/beet/commit/a3a39fe2cc6668b8e098b6bb597f3febb35119a1))
* Add ctx.validate() ([`e1210cf`](https://github.com/mcbeet/beet/commit/e1210cf287127e08abccd3040f9ef602d1392485))
* Add stable_int_hash() utility ([`e08d004`](https://github.com/mcbeet/beet/commit/e08d004d818652d6301f885171ebef9cfaa2875e))

Feature
* Add beet.contrib.load_yaml plugin ([`86af226`](https://github.com/mcbeet/beet/commit/86af2264faa9f9484896fbe925e9d61def648186))
* Make it possible to pass a custom callback to ensure_serialized() and ensure_deserialized() ([`d75648b`](https://github.com/mcbeet/beet/commit/d75648b9f23cd66e87b79dd663370f8288291cd3))

Fix
* Show template filename in traceback ([`695fab6`](https://github.com/mcbeet/beet/commit/695fab62cea3e0a3c2dd53128d2769e40fc998ff))

Feature
* Make pillow optional ([`9778883`](https://github.com/mcbeet/beet/commit/977888375b0ca3ca334a391b0ab4bc4a1ed9a0d5))