docs: Add libteletone back to core API documentation

Right... this one is actually part of the core
(.o files included in libfreeswitch).

There are a few more libs included like this, but none
of them should be for external use.
Signed-off-by: Stefan Knoblich <s.knoblich@axsentis.de>

docs/Doxygen.conf

@@ -568,7 +568,7 @@ WARN_LOGFILE           =
 # directories like "/usr/src/myproject". Separate the files or directories
 # with spaces.
 
-INPUT                  =../src
+INPUT                  =../src ../libs/libteletone
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding, which is