Renaming AppMode to SimpleMode

* This makes naming consistent since we already have SimpleAction.
* There is now a separate module for SimpleAction, this allows to depend
  only on parts of the API you actually need.
* Updating examples.
Slightly changing sematics of runApplication

If function passed as first argument returns "Just (acation, config)"
then passed endomorphism is applied to it. This way command line options
can have higher priority then e.g. configuration file.
Exporting forgotten UsageInfoConfig

* It doesn't make sense to not export UsageInfoConfig data type.
* Function usageInfo was renamed to formatUsageInfo to be consistent
  with the rest.
Updating examples for version 0.3.0.0