Don't build documentation for non-public directories

[bordoley]

I have a bunch of my modules in my bsb project that reside in directories marked not public in my bsconfig. Ideally these would not be documented either in the output of docre.

[bordoley]

I'll take a look into this in the coming week or so. Note to self:

"It would involve modifying "getSourceDirectories" in CliToInput.re to include an optional module whitelist (from the "public" field)."