Details:
- added support for complex numbers as distinct from floats:
%[efg] allows complex; %b does not.
- %p: only Signature, Map, Chan, Slice, unsafe.Pointer allowed.
- %s: allow []byte.
- allow a verb to match map[K]V and []T if it matches K/V/T,
e.g. %d now matches []int. i.e. matching is recursive.
- use go/types' constant folding. literal() is gone.
- group cases together.
Added tests.
R=gri, r
CC=golang-dev
https://golang.org/cl/10895043
25f3e0fbde