CLI usability improvements / modernization

[andypiper]

A few things to add here for tracking purposes:

• twurl help returns "Invalid URI detected" - easier to alias this to the same result as -h or --help
• twurl -v could include the Ruby runtime version, for debugging / troubleshooting purposes (we already send this as part of the user-agent string on the API request)
• twurl -U (the ability to disable SSL) should be removed, since TLS is always required.
• twurl -T prints out the markdown format of the tutorial, and could be reformatted. It should also provide examples for API v2.
• ~~twurl -u (username) is strictly not required.~~ (incorrect, it is needed for selecting bearer tokens)