Developers: Updates for civix and cv

cv (https://github.com/civicrm/cv) and civix (https://github.com/totten/civix) are Unix/CLI tools for developers. cv provides access to your Civi site on the command line, and civix generates skeletal code for new extensions. We've had a few recent updates to each of these tools, so I wanted to introduce cv more formally and then recap some of recent improvements for each tool.