Add an 'open' command to open the specified error in your browser

Add:
 * Launchy gem for cross-platform browser 'open' functionality
 * New 'open' command to open the specified error (with optional notice)
   in your default browser
Merge pull request #21 from kevinjalbert/add-ability-to-open-error-url

Add an 'open' command to open the specified error in your browser