Implement receiving of changelog

[mellowagain]

The osu! client shows on a Beta and Cutting Edge update the changelog on start in the bottom left corner. This is fetched using the /p/changelog route.

I propose the implementation of this in connection with the Git commit history of Shiro.

[mellowagain]

The format for /p/changelog is each line is a new changelog, with each line having either two three arguments separated by a tab character (\t):

• Type (One character, either + for "Added", * for "Fixed" or any other character for "Misc")
• Author
• Message

For example:

*	peppy	Bug fixes and minor improvements.

Note: /p/changelog without the &updater=3 argument just redirects to the osu-web changelog page, even with osu! user agent.