feat: generate docs for jsii submodules

[Chriscbr]

Fixes #1

• Adds docs for all classes, structs, interfaces, and enums in submodules
• Changes class initialization examples to include submodule paths, e.g. new foo.MyClass(...) instead of new MyClass(...)
• Updates class docs to include a "submodule" section if the class has an associated namespace
• Modifies tsconfig to allow using flatMap

I tested this with docs for projen, and the would-be updated docs are here: https://gist.github.com/Chriscbr/41f7f7e7d1d358dc6ebf0f8cb277b937

[eladb]

The names in the TOC tables should also include the submodule prefix.

For example, in projen, the Github class should be named github.Github