Passing multiple apidoc_module_dir's

[rahasurana]

We have a centralized doc generation where sphinx-apidoc is called on each repo and the generated rst files are used to generate the documentation,

Given this is a pre-stage operation done outside sphinx, current extension seemed like a good way to avoid the pre-stage creation of rst. Only caveat here is that apidoc_module_dir only accepts a single path. Can this be enhanced to accept a list of paths?