go spec: clean-up and consolidation of spec with implementation
Specifically:
- introduced notion of "underlying type"
- removed notion of type compatibility
- consolidated rules about assignment compatibility in
assignment compatibility section
- be consistent with specyfing that nil is the value
for uninitialized variables that can be nil (this
was not specified clearly for pointers, functions, interfaces)
- added/fixed various related links throughout
- clarify language on conversions
R=rsc, r, iant, ken2
CC=golang-dev
https://golang.org/cl/
1536041