Use the new command registration chaining capabilities to eliminate
the foo_register_commands helper, folding its remaining command
handler setup into the hello_command_handlers registration array.
Adds the foo/bar commands to provide more working examples of command
argument parsing, including the new handle_command_parse_bool helper.
Updates hello command help text to provide useful information.
The hello module provides the 'hello' command, printing a greetings
to the command console. It can grow to serve as pedagogical example
of services that OpenOCD developers should use: a runnable style guide.
