Add ranging API

Also restrict black boxes to not allow hardware inside of them since it was
being silently dropped anyway.

Resolves #289

Workaround for:
http://www.veripool.org/issues/1101-Verilator-Fix-SmallName-for-ParamTypeDType

Also, remove no-longer-special case for n=1.

Eliminate some doc warnings

Implemented by adding a Boolean to check for alternating invocations of object
Module.apply and the constructor of abstract class Module.
Fixes #192

Prefix temporary names with underscores so Verilator won't trace them
Use verilator argument "--trace-underscore" if you want to trace these
signals