fix codestyling a bit
fix issue #6: add support for 'use' methods

- add support for 'use' methods
- make 'use' methods invalid in the strict mode
- add deferred key for 'use' that should be defined after the routes
- add support to forced/locked keys for deferred (only) middleware
- fix README.md: add 'Middleware with USE method (loggers, error handlers, etc)' paragraph