Various changes to documentation framework.

- Reorganize top-level 'doc' Makefile target so submodules can easily
  add their own doc-generating routines to it.  e.g. the Bro project
  makes a placeholder 'doc' target, then adds 'restdoc', 'sphinxdoc';
  later Broccoli can add it's own target as a dependency for generating
  API docs.

- Fixed generated docs for BIFs not being organized under a base/
  subdirectory like the original source files.

- Fixed documentation style for function parameters not applying to
  functions declared as record fields.

- Misc. script documentation tweaks to address warnings given by Sphinx.

doc/scripts/genDocSourcesList.sh

@@ -73,7 +73,7 @@ bifs=`( cd ${sourcedir}/src && find . -name \*\.bif | sort )`
 for file in $bifs
 do
     f=${file:2}.bro
-    echo "rest_target(\${CMAKE_BINARY_DIR}/src/base $f)" >> $outfile
+    echo "rest_target(\${CMAKE_BINARY_DIR}/src base/$f)" >> $outfile
 done
 
 scriptfiles=`( cd ${sourcedir}/scripts && find . -name \*\.bro | sort )`