Development of fmbtx11_agent started

fmbtx11_agent implements event synthesis and X11 screenshots with
minimal other dependencies. Helps building agents
pythonshare-server for operating systems that run X.
pythonshare: server supports stdin connections

HOSTSPEC scheme shell:// added. This combination enables running
Python code and expressions directly on other hosts with
pythonshare-client \
    -C 'shell://ssh host:pythonshare-server -p stdin' \
    -c CODE
without setting up server, forwarding ports, etc.