CodeMaid API header cleanup.
More API header formatting cleanup.

Fixed a few bad formatting changes CodeMaid made, wrapped most of the
code to 80 characters (not the error descriptions, I think it's easier
to read them as-is), and tweaked function comments to make parameter
documentation easier to read.
Removed Message::tag.

Also hosed pretty assignment block indents. Thanks, CodeMaid! >:| I
can't figure out how not to make it do that, the extension is too useful
otherwise though.
Improved some masterlist update error messages.

Also CodeMaid tidied up a few initialisers.
Added sorting and update functions to API header.

As yet unimplemented.
Fixed some Doxygen errors.
Moved Doxygen index into API header.
Implemented loot_apply_load_order.

Also improved constness of parameters.
Implemented loot_sort_plugins.
Merge branch 'api-sorting' into v0.7-alpha

Conflicts:
	src/api/api.cpp
	src/api/api.h
	src/backend/git.cpp