[PATCH] squidclient modular redesign

I am trying to update squidclient support multiple protocol request
messages (HTTP/1, HTTP/2, HTCP, ICP).

The attached patch begins breaking the existing code into modules. The
"ping mode" operations and command line processing are broken out from
the main squidclient.cc into Ping.* files.

To keep the tool code files clearly identifiable now that they are
multiplying they are shuffled into tools/squidclient/

A mechanism is added to allow each module to have its own option set.
Ping-specific short command line options are now only parsed after a
mode flag (--ping) is presented. This frees up the -g and -I options for
use by other non-ping modules in future.

Amos