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.

Makefile

@@ -13,15 +13,14 @@ all: configured
 install: configured
 	( cd $(BUILD) && make install )
 
-clean: configured
+clean: configured docclean
 	( cd $(BUILD) && make clean )
-	( cd $(BUILD) && make docclean && make restclean )
 
 doc: configured
 	( cd $(BUILD) && make doc )
 
 docclean: configured
-	( cd $(BUILD) && make docclean && make restclean )
+	( cd $(BUILD) && make docclean )
 
 dist:
 	@./pkg/make-src-packages