cli: add minimal line completion to the CLI
cli: add minimal line completion to the CLI

Borrowed from:
https://github.com/svaarala/duktape/blob/master/examples/cmdline/duk_cmdline.c

Fixes: https://github.com/saghul/sjs/issues/45

joegen/sjs,saghul/sjs,joegen/sjs,saghul/sjs,saghul/sjs,joegen/sjs,saghul/sjs