devel/cl-flexi-streams{,-*}: New ports

FLEXI-STREAMS provides "virtual" bivalent streams that can be layered on
top of real binary or bivalent streams. These streams enable reading
and writing of character data in various single- or multi-octet
encodings, which can be dynamically changed. The package also includes
in-memory binary streams, similar to string streams, for efficient
handling of binary data.

Sponsored by: The FreeBSD Foundation