BundleBridge and CrossingWrapper API cleanups (pt 2)

diplomacy: desugar BundleBridge -- it was too confusing

Sometimes more typing is better.

Clock Crossings: make API more flexible with CrossingHelper

chisel3 changes:
* Direct translation of ChiselIR to FIRRTL
* Driver support for emitting Protobuf
* Better error message for calling return in a when block

firrtl changes:
* Escaped single quotes supported in ExtModule RawParams
* Partial fix to RemoveWires when reg depends on wire
* Parser performance improvements
* Protobuf serialization and deserialization
* Fix annotation renaming for empty aggregates
* Improved code generation for smem wmode and [w]mask ports
* InferWidths performance improvement
* Some user errors no longer reported as "internal errors"
* Add annotation for combinational dependencies between top-level ports
* InstanceGraph is now deterministic

chisel3 changes:
* Direct translation of ChiselIR to FIRRTL
* Driver support for emitting Protobuf
* Better error message for calling return in a when block

firrtl changes:
* Escaped single quotes supported in ExtModule RawParams
* Partial fix to RemoveWires when reg depends on wire
* Parser performance improvements
* Protobuf serialization and deserialization
* Fix annotation renaming for empty aggregates
* Improved code generation for smem wmode and [w]mask ports
* InferWidths performance improvement
* Some user errors no longer reported as "internal errors"
* Add annotation for combinational dependencies between top-level ports
* InstanceGraph is now deterministic

Richer DTS

Otherwise you end up with SPI and CPU addressses in the address map.

This makes reg formatting respect #address-cells.

Busses like SPI do not have address ranges, but simple integer indexes.
This helper method makes code for these busses more readable.

This can greatly simplify the description of dependant busses, like SPI.

Sometimes there is no address information to bind, so just create
these devices with a stub binding to ensure they appear in DTS.

When dealing with frequencies, Double is a better, but in DTS we will need
to still represent this using an Int.  This helper makes it less painful.

Every Device creates a label, thus checking for labels ensures we will never
elide a device's DTS node, even if it is empty.  This is useful to create,
say, an empty "/chosen" to work around an old kernel bug.

References are written: key = <&label>;
Aliases are written:    key = &label;

References compile to a phandle integer value.
Aliases compile to a string path name.

Bind DTS aliases

This makes it possible to bind clocks to most DTS devices