Some doxygen symbols do not resolve

[bennylp]

1. Some macros wong resolve, e.g. PJ_HAS_TCP. Sample page: Writing guide.

   Suspicion: maybe because these macros have been declared somewhere else, e.g. by ./configure?

2. Some enum values must be explicitly specified with the enum name, otherwise they won't resolve. For example, in Video user's guide, PJSUA_CALL_VID_STRM_ADD must be explicitly written as pjsua_call_vid_strm_op::PJSUA_CALL_VID_STRM_ADD.

   Suspicion: is it because the enum was declared in enum typedef?