opensips: make-docs; also cleanedup xlog's
opensips: prep for new compiler: mediaproxy as conditional

We will no longer rely on the compiler to remove inexistent routes.
opensips: initial-forwarder -> initial_forwarder
opensips: invite-handler -> invite_handler
opensips: invite-trunk-drouting -> invite_trunk_drouting
opensips: try-* -> try_*
opensips: *-nat -> *_nat
opensips: register_record_route moved out
opensips: migrate register* to new compiler
opensips: couple internal route names rewrites
opensips: force user to specify either `authenticate` or `authenticate-disabled`.

This is a backward-compatibility BREAKING change. If you use a non-standard `recipe`, then you MUST ensure that one of `authenticate` or `authenticate-disabled` is present in the recipe (for most recipes; `authenticate` is called from `non-loose-route`).
opensips: new compiler no longer trims calls to missing `route` statements.
opensips: new fragments cross-reference document.

Run `make-doc.sh` to re-build it.
opensips: compiler should handle two-level `if` macros
opensips: more route names cleanup
opensips: avpops module is required in generic (and others)

Note: make sure `generic` is listed before `avpops_db` in your recipes.
opensips: use standardized names for uac_auth's username, etc. AVPs.
opensips: registrant: make sure we properly use the new auth code in b2b apps.
opensips: the new tests help figure out plenty of compile-time issues, hooray!
opensips: optional Makefile to cleanup the test directory