picolisp: include httpGate tool

https://software-lab.de/doc/httpGate.html

httpGate is a central element of the PicoLisp application server
architecture. Its purpose is to perform the following tasks:

* Provide a single application entry port (e.g. 80 or 443).
* Allow PicoLisp applications to run as non-root.
* Start application servers on demand.
* Handle HTTPS/SSL communication.