avro

AVRO-863. C: Schema resolution using new value interface

This patch adds the avro_resolved_reader_t and avro_resolved_writer_t
classes, which handle schema resolution using the new avro_value_t
interface.  The resolved reader type wraps an existing value as the
"writer schema" side of schema resolution, and provides a view into the
wrapped value as if it were an instance of the reader schema.  The
resolved writer type does the inverse; it wraps an instance of the
reader schema, and lets you write into that value as if it were an
instance of the writer schema.


git-svn-id: https://svn.apache.org/repos/asf/avro/trunk@1175832 13f79535-47bb-0310-9956-ffa450edef68