Improve output when --dump is given

* Put newlines after each GET request
* Make sure we dump the request even when a POST produces an error
* lib/razor/cli/navigate.rb (extract_command): do not use arguments as values

When users pass '--arg1 --arg2', we do not want to treat '--arg2' as the
value for argument arg1. Instead, arg1's value is nil.
Add a 'boolean' argument type for commands

This makes it possible to pass '--flag' in a command and have { 'flag':
true } show up in the JSON

Fixes https://tickets.puppetlabs.com/browse/RAZOR-110