add avro schema to support other languages

Add [Apache Avro](http://avro.apache.org/) protocol schema for other [Supported Languages](https://cwiki.apache.org/confluence/display/AVRO/Supported+Languages).It was only a partial modification to the attempt. Not centain if such avro schema can fit this project.

```
$ nosetests test/test_avroproto.py
....
----------------------------------------------------------------------
Ran 4 tests in 0.002s

OK
```
@hoffmabc [Shifu](http://kungfupanda.wikia.com/wiki/File:ShifuPreparesToAttack.png) will be installing [pylint](http://www.pylint.org/) on the build tomorrow. If this won't make you hate me, nothing will.

(Sneak preview: https://github.com/Renelvon/OpenBazaar/tree/pylint_checks)