Teach qdoc to count intermodule links and generate a report

qdoc maintains a separate "AST" tree for each module. It has the information required for keeping track of the numbers of inter-module links, but it currently doesn't do this. A report of the inter-module links would be useful for two purposes.

First, it will reveal the modules missing from the "depends" list in the qdocconf file. Second, it will allow ordering the module names in the "depends" list for the optimal searching.