Directly subclassing Iterable is lazy-ish, but if you call any operation
on the resulting value (eg. map or ++) it will evaluate the Iterable and
return a List.

Transformation of mem readwriters whose address contain references to
readwriters of mems declared before it would contain invalid references
to untransformed memory readwriter, as the connection is not transformed.
This commit fixes this issue.

This will make it easier to compile circuits with
older compiler versions.

* [smem] fix read-under-write serialization

Also adds some tests for the parser and
the serializer.

* Serializer: always serialize smem ruw behavior

* test: simplify smem test circuit

* allow for zero-width integer literals
* CheckWidths: ensure that width is non-negative

Also get rid of whitespace-only lines that were emitted after every when
block.

This is needed for emitting modules that serialize to Strings larger
than 2 GiB (the maximum String size on the JVM). It includes
micro-optimized logic for turning arbitrarily nested when scopes into
Iterable[String].

Ever since introducing the Listener, the firrtl Parser now can hit
errors in the code converting from concrete syntax to abstract syntax
that may be due to syntax errors. These errors are essentially broken
assumptions about the structure of the parsed code because there is an
error. These errors are reported before the standard ANTLR syntax errors
are aggregated and reported, and thus could result in less than elegant
error messages (eg. NullPointerException). Now, the Parser will mask off
such errors in the event of standard syntax errors caught by the
ANTLR-generated parser.

This commit also cleans up some ParserSpec tests slightly to make the
ScalaTest style more canonical.