Add support for Deno

[philc]

Deno is a newer alternative to Node, by the same author.

js-comint ostensibly supports multiple JS engines, but there are some places in the code which are hard-coded to support node.

For instance, the function js-comint-start-or-switch-to-repl appends -e to any user supplied command line arguments (-e is "eval-script" in Node), and this is an unsupported command line option in Deno.