X11 remote support.

Still need a better story for setting DISPLAY on remotes...
De-Titlecase modifier names in example.conf.

xmodmap prints them in all lowercase, so I figure that's the
"canonical" format for them.
Add simple-minded kvmap.[ch].

Provides a basic key-value map interface to be used for remote
configuration parameters.
Add remote config parameter-passing mechanism.

SETUP message's extra buffer provides a flattened kvmap of arbitrary
config settings.
Set X11 remotes' DISPLAY from a config param.

No longer hardcoded to DISPLAY=:0; config should instead specify
'param["DISPLAY"] = ":0"' (or similar) for the relevant remote.