libcli: new package

Libcli provides a shared library for including a Cisco-like command-
line interface into other software. It's a telnet interface which
supports command-line editing, history, authentication and callbacks
for a user-definable function tree.

[Thomas: rewrap Config.in help text.]

Signed-off-by: Steve James <ste@junkomatic.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>