doc/man: document LTTng-UST 2.13

Significant changes:

* Prefix all macro/definition names with `LTTNG_UST_` or `lttng_ust_`
  where needed.

* Prefix all log level definitions with `LTTNG_UST_TRACEPOINT_LOGLEVEL`.

* lttng-ust(3):

  * Add "Compatibility with previous APIs" section to explain
    the new `LTTNG_UST_COMPAT_API_VERSION` definition.

  * Document the new tracepoint class provider name parameter of
    `LTTNG_UST_TRACEPOINT_EVENT_INSTANCE()`.

    Update examples accordingly.

* Mention `liblttng-ust-common` where missing.

* tracef(3), vtracef(3), tracelog(3), and vtracelog(3) now indicate that
  the macros are part of version 0 of the LTTng-UST API, albeit still
  available, and point to lttng_ust_tracef(3), lttng_ust_vtracef(3),
  lttng_ust_tracelog(3), and lttng_ust_vtracelog(3).

* New lttng_ust_do_tracepoint(3), lttng_ust_tracepoint(3),
  and lttng_ust_tracepoint_enabled(3) manual pages which source
  lttng-ust(3).

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I07d6ace0d6f219c36d7c99a455726bbf4b0736a2