Javadoc remapping support

[ramidzkh]

Remaps method and field references in Javadoc. Still needs better testing (e.g. constructors)

[jamierocks]

I've just been testing this locally, and it seems your #rewrite() method isn't required - is there any particular cases that resolves?

edit: me and Minecrell discussed this, and we're confident it's not required.

[jamierocks]

Merged with https://github.com/CadixDev/Mercury/commit/6379e58e914160b5c9d9f4e822d5269586e2260b.

[liach]

nice, thanks ramidzkh!