v1.4.0-RC1

(#157) Make DspComplex multiplies use growing addition.
DspComplex relies on using the underlying Ring's multiplication. For
UInt, SInt, FixedPoint, etc. these additions wrap instead of grow. For
our implementation of complex multiplication, growing is more desirable
than wrapping.

(#162) Add test for FixedPoint's asReal() implementation

(#189) Add saturating addition/subtraction.
This implements saturating addition/subtraction with inferred widths.

(#206) Bump for newer rocket, rewrite chain connections in cleaner way

(#208) Bump Rocketchip to June 2020