kiji-mapreduce: KIJIMR-262. Tool to rewrite cells in a Kiji table

 - Pivot M/R job that rewrites cells in a column of a Kiji table.
 - Rewriting rules are specified through an Avro record serialized in the Hadoop configuration.
 - Rewriting rules are chained to allow the decomposition of incompatible changes in a sequence compatible changes.
 - Unit-tests.

issue: https://jira.kiji.org/browse/KIJIMR-262
review: https://review.kiji.org/r/1618
commit: https://github.com/kijiproject/kiji-mapreduce/commit/e3caea041c8975f9d4fba5a8e46d7d583302644d