Initial beta release

This initial release is intended to mark a stable API. We reserve the right to make API-incompatible changes if absolutely necessary for bug-fixing, but that should be unlikely.

Some features included:

• Go code generation with a natural mapping between Avro schemas and Go types
• auto-generation of Avro schemas from Go types
• support for the Avro schema registry
• support for the logical type timestamp-micros as the Go type time.Time.