Preview release with simplified API and bug fixes

CloudWatch Logs API support improvements.

• When a query chunk goes into a bad state ensure we always attempt to stop it using StopQuery.
• Re-enable Preview mode support if query text uses stats command.

Incite library API improvements.

• Remove special case unmarshaling of []byte.
• Remove excess interfaces Queryer and Reader.

Other improvements.

• Add more example tests for Unmarshal.
• Simplify *stream.Read implementation by replacing channel with condition.
• Fix bugs in Preview mode result translation logic.
• Fix bugs where chunks weren't always being closed properly.
• Fix some annoying Go-style bugs with closure and range loop variables, improving stability of test framework for scenarios.
• Just generally improve documentation and test coverage.