Support field renaming for Avro read schemas, by means of
field aliases.

Avro 1.7.6 is required since it fixes https://issues.apache.org/jira/browse/AVRO-1433
But note that this is only to allow the test to run correctly.
Add explicit blank namespaces to account for change in AVRO-1295 in Avro 1.7.5.
Merge pull request #303 from tomwhite/avro-read-schema-aliases

Avro read schema aliases