New categories

In effort to provide some organization for our forums, I’ve introduced the following categories:

Help - for topics requesting help using beets. This also includes the ability to mark answers as the “solution” for a topic, marking the topic as “solved”.
Development - for topics related to the development of beets
Show and Tell - as discussed here, this is a category for users to show off how they use beets! Any topics have the potential to be featured in the Advanced Awesomeness section of the docs.