Add -p, —prototype command line option

 - Enable the option that was there
 - In fetch_latest_tag:
    - Use parameter to method rather than instance variable for repo
    - Check that we get a “200” response - otherwise error out and let user know the response code
    - Check that we have at least one tag - otherwise error out and let user know about tags
Noted that you need wget installed - not there on new macs
Add notes to README.md and amend output for custom prototype

 - Describe usage with -p
 - Note that the repo must be tagged
 - Note that custom repos should not have binary files, due to use of sed

 - Output after generating from custom prototype reduced to basic congrats - can’t assume any of the next steps will be valid.
Changelog...