cmd/compile: introduce printer for internal formatting; use in jconv
Starting point for uniform use of printer in fmt.go.
It provides a hook to store additional state (and
remove global variables) and should also be more
efficient and cleaner than the mix of string concatenation
and bytes.Buffer use we have now.
Change-Id: I72de14b01850cca32d407a1cb16c894179ea8848
Reviewed-on: https://go-review.googlesource.com/27916 Reviewed-by: Matthew Dempsky <mdempsky@google.com>