v doc improvements

[radare]

I'm trying to learn about the compiler internals and having code autocompletion and other IDE integrations would help me on understandimng better the internal apis.

v doc works well for the web and the current output with the function and struct signatures is nice, but it doesn't work across different modules or works recursively.

So my idea is to have something like v doc -r v and this will show the documentation for v.builtin v.ast v....

Also i miss the abilty to enumerate all the modules