Namespace ust-fork symbols

Namespace ust-fork symbols

Namespace the public symbols used by liblttng-ust-fork and move them a
more appropriatly named header.

The major SONAME bump to '1' gives us the opportunity to properly
namespace some older parts of the API.

Change-Id: Ic44998cbf77c3ae8cd7e73c9ad789d743cefdd05
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>