Add avro-reflect support

[asfimport]

Parquet's Avro object model currently supports only specific (generated from Avro schemas) and generic objects, but Avro has support to work with any object through reflection.

Reporter: Ryan Blue / @rdblue
Assignee: Ryan Blue / @rdblue

Related issues:

• Avro object model should use Utf8 (is depended upon by)

PRs and other links:

• PR #165

_{Note: This issue was originally created as PARQUET-243. Please see the migration documentation for further details.}

[asfimport]

Ryan Blue / @rdblue:
Implemented in PR #165.

[asfimport]

Ryan Blue / @rdblue:
Merged #165. Thanks for the review, Tom!