Add search filters for changelog's entry categories

[Torphage]

I really like the changelog listing that currently exist, but finding what you want is harder than it has to be. It would be nice to be able to see all the progress that have been made within a specific part within osu! development. But as of now you have to go through each update, one by one, in hoping to find what you are looking for. To be able to filter out only the categories you are looking for would speed up the process of finding other contributions within a chosen area.

Personally I would like to see what progress have been made with skinning on osu!lazer, to be able to go through other's contributions in order to see how different parts were implemented.
But currently I have to go through every page in hoping to find the previous update on skinning, and skinning isn't the highest priority which makes finding a single one hard. Many of the pull requests on Github are not labeled, which exclude looking through Github issues an alternative.

[peppy]

Changelog isn't really made to show progress on tasks. We use github for that (milestones / issues). You might be better off finding what you want there.