Generate Doxygen files for Trick headers

Since the headers moved to include/trick, the Doxyfile's INPUT needs to
be updated.

doxygen/Doxyfile

@@ -680,6 +680,7 @@ WARN_LOGFILE           = $(TRICK_HOME)/doxygen/warning_msgs
 
 INPUT                  = $(TRICK_HOME)/doxygen \
                          $(TRICK_HOME)/trick_source
+                         $(TRICK_HOME)/include
 
 # 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