Fix for Issue 1125 - Bootstrapper throws with multiple RootPathProviders
Modified MultipleRootPathProvidersLocatedException following review

See comments on https://github.com/NancyFx/Nancy/pull/1126
Minor tweaks to the code and formatting
Introduced BootstrapperException and cleaned up code
Fixed output format bug
Clarified ScanMode member descriptions
Excluded Nancy.Testing from assembly scanning