Major changes

• renamed the group id from com.softwaremill.tapir to com.softwaremill.sttp.tapir (organization)
• renamed the main package from tapir to sttp.tapir (see sttp-client/#288)
• Codecs are parametrised with a CodecFormat, instead of a MediaType (however, codec format still includes a media type)
• using sttp model (which is shared with sttp client)
• changed SchemaFor[T] into Schema[T]. Previous Schema datatype now is SchemaType (#247)

And some minor changes :)