Merge pull request #299 from tomwhite/avro-fill-in-default-values

Fill in default values for new fields in the Avro read schema
Merge pull request #303 from tomwhite/avro-read-schema-aliases

Avro read schema aliases
wip
Fix warnings and imports. Simplify handling of fixed.
Add TODOs
Add a test
Add primitive types
Support byte array
Add map
Array
Add test for short[]
Revert incompatible change to fixed.
Tidy up
Add char - requires AVRO-1282, 1.7.5
Fixes after rebase. Char is not working due to weird bug (in Avro) where other fields (boolean, byte) are getting reset to default when the char field is set via reflection.