This currently implements exactly what Driver did before, but in a
manner such that other non-RocketChip users can start implementing other
pass managers.

Fixes #308 
Fixes #193 

Style Fixes for Memory Passes

* fill empty module body with "begin end"

apparently vivado treats an empty module as a black box and triggers an error

* Changed empty module to use always @(*) begin end

Despite the fact that LinkedHashMaps preserve insertion order in traversal, it
appears that .keys and .keySet return Sets that do not provide the same
guarantee

Style Fixes for Compiler, LoweringCompiler, WIR

* Addressed the fact that a node can be connected to itself (updating reg)

ceil(log(x) / log(2)) does not, in general, round to ceil(log2(x)).
I noticed this because of #297.

Case object for WVoid WInvalid

use case object for Kind

More passes cleanups

no vars for mname, info

More utils cleanups