Util: add support for config validation
Example: add validation function
Utils: add MonadIO constraint to ConfigValidation
Add module Utils.Validation with functions for validating configuration values
Utils.Http: add validation functions
Example: get rid of some compiler warnings
Example: fix example test by wrapping it's main function into a test function
Utils.Http: fix compilation for GHC < 7.8
Merge pull request #2 from alephcloud/feature/validation

Feature/validation