Now, instead of using Utils.cpp's AccountCachePath and AddOnCachePath,
and add-on should implement ChatProtocol::SetAccountCachePath and
ChatProtocol::SetAddOnCachePath.
In addition, most path-related functions in Utils now return BPaths― and
some of interest to chat add-ons can accept the path given by
ChatProtocol::SetAccountCachePath as the main argument.
Some chat protocol messages' names have been changed to more fitting or
consistent names― e.g., "IM_AVATAR_SET" to "IM_USER_AVATAR_SET", or
"IM_CONTACT_LIST_*" to "IM_ROSTER_*" (to agree with Cardie's usage of
the word).
The API version has been bumped― for the forseeable future (at least
several months, I promise!) no compatibility-breaking changes will be
introduced. Until then, any new feautures or message slots will be
additive and optional.