Issue #7: Updated SetCacheKeys method to consider QueryStringKey value.
Refactored WebApiHelper from WebApiCacheAttribute.
Added test methods for helper class.
Fixed typo.
Updated README.md.
Added test methods for WebApiCacheHelper.
Added test methods for WebApiCacheHelper.
Updated test methods for WebApiCacheHelper and WebApiCacheAttributeTest.
Updated README.md
Versioned up to 1.5.0.0