symbol->png will also accept fpng as a stream
added encode-png-stream and encode-png-bytes-stream
Merge branch 'patch-1' of https://github.com/okflo/cl-qrencode into support-streams

Conflicts:
	image/png.lisp
merge pull request #2 from okflo, resolve conflict

ENCODE-PNG-BYTES should have been deprecated, so we don't
export ENCODE-PNG-BYTES-STREAM any more
Merge branch 'okflo-support-streams'