Pre 1.0 API cleanup

[bartelink]

This is the result of a read-and-review as I'm using this in a client template. I've applied the following:

• intentional minor breaking changes to remove arbitrary deviations from Confluent.Kafka defaults:
  • offsetCommitInterval - the frequency of commits of consumer offsets increases to 5s to align with CK default (was 10s for historical reasons)
  • fetchMinBytes default is now 1B (was 10B for historical reasons)
• adding information as to how the settings used relate to documented Confluent.Kafka default values
• removed egregious setting of CK Config values to null
• exposed an Inner on Producer/Consumer to enable custom client logic without having to fork
• F# syntax conventions - no egregious val usage, no curried members