Update README.md

adding some more instructions to README
changing the sweeper job to use SchemaValidator to determine if the key is compatible with topics schema.
updating avro version
Fix the offset calculation, we don't use beginOffset anymore
Add classpath/classloader debugging on avro classes
Add classpath debugging for avro classes for sweeper
Deal with property cache.jar.filter.list can be non-existent
fixing schema projection bug
Minor fixes to fix recent merge from upstream master"
Camus sweeper azkaban job