plow* (command-line parsing): create early options

Parsing process is now in 4 steps instead of 3.
Early options are --help, --version and --no-plowsharerc.
These option are availalble for command-line only and will be ignored in configuration file.

This requires some more cpu processing, but help message is now fast.
This will be restricted to plowshare4 only.
2shared: add probe support
plow*: add --plowsharerc=<config file> command-line option

Documentation  (manpages, bash completion) updated.

This will be restricted to plowshare4 only.