More design rationale for Vec

Further testing improvements

Fix new style errors

Style fixes for test code

Testing improvements fixing 4 broken tests and reducing runtime

In addition to removing all the extraneous Driver invocations that created various top-level Parameters instances,
this commit also lays the groundwork for stanza-firrtl/verilator based testing of Modules that extend BasicTester.

The execution-based tests have been updated accordingly. They will only succeed if firrtl and verilator binaries have been installed.
Further work is needed on individual tests to use assertions instead of .io.error.

Add compile and checkstyle make targets.

Add documentation on some non-intuitive parts

Remove implementation details from scaladoc.

You didn't want it, so Imma getting rid of it...

Add Scalastyle rule to check for lines ending with ; and fix some instances

Scalastyle ignore ## and printlns in Error.scala

Deprecations and better documentation for Aggregate.scala

At least one of these is incorrect.

Break out Utils.scala into smaller portions

Fix whitespace in Bits

Move Cat into utils

Resolve some review todos in Bits

Fix review todos in BitPat.scala