First version of the new implementation has been committed to the svn
repository. It should fix most of the bugs with the old API. There
will be more changes, but the core is there now.

Fixes:
1. POST should work now
2. Full control over API authentication and user authentication
   * these two have been separated so you can now implement whatever
API authentication you want (with 2 default options)
   * you can control what authentication is used by the REST service
with a plugin hook
3. You can throw exceptions in your exposed functions and they are
turned into API results for you
4. Several other bug fixes

Outstanding issues:
1. Elgg's session implementation currently makes it impossible to use
an auth token while a user is logged in using browser
2. XML output still has some issues (is it too verbose with all the
info on type?)
3. I'm still working through centralizing the endpoints. I don't plan
to implement any additional services but make it easy for anyone to
add a service (example: maybe someone wants json as both the input and
output of a service)