Our plans for 0.2.3 are mostly clean up - remove h...

# ktor

[orangy]

Our plans for 0.2.3 are mostly clean up
- remove host api from core module, so they are properly separated
- change user-application from inheriting Application class to implementing ApplicationFeature (cleans a lot of mess, makes it all uniform, allows for multi-application composition in single host, etc)
- unify various features into ApplicationFeature (such as CORS for example)