An Omniauth 1.0 Strategy for yahoo

For more information see the following:

 * https://github.com/intridea/omniauth/wiki/List-of-Strategies

Release notes:

 * Version 0.0.4
 
  - Added skip_info? patch from mkdynamic

 * Version 0.0.3
 
  - Added primary email as per famoseagle
  
 * Version 0.0.1

   - First cut