utf8: add InString routines for decoding in strings

utf8: add InString routines for decoding in strings
reflect: add InterfaceValue.Get(), remove Empty
strconv: add Quote, CanBackquote
fmt:
	* %q go-quoted " string
	* %#q go-quoted ` string if possible, " string otherwise
	* %x hexadecimal string
	* anywhere a string is okay, *[]byte is okay
	* flags # 0 - + space
	* print value inside interface, not interface itself
	* tests

R=r
DELTA=756  (597 added, 121 deleted, 38 changed)
OCL=19888
CL=19916