It includes a reason code that makes it possible for the clients to be
more reasonable about error messages.
The reason code is essentially copied from the VPN, plus three more
reasons that were useful for non-VPN connections.
This makes it easier to install the files with proper names.
Also, it makes the makefile rules slightly simpler.
Lastly, the documentation is now generated into docs/api, which makes it
possible to get rid of the awkward relative file names in docbook.