renamed "handlers" module to "handler"
Revert "renamed "handlers" module to "handler""

This reverts commit a6aae5d70d5d2f0aa65124a1cd9e8a1c47c3c010.
reworked code structure
optimized App.route method
reworked examples
fixed complex example
yet another fix of complex example
renamed module with handler's tests
fixed basic example