SCHEMA-492. HBaseSystemTable.install() uses a deprecated HTableDescriptor constructor.

issue: https://jira.kiji.org/browse/SCHEMA-492
review: https://review.kiji.org/r/950
Remove version number from readme.
SCHEMA-536. Centralize ProtocolVersions definition and documentation.

 - Moves all declared ProtocolVersion into utility class Versions.

issue: https://jira.kiji.org/browse/SCHEMA-536
review: https://review.kiji.org/r/988
SCHEMA-530. Implement developer validation mode

- CellSpec has an optional column URI.
- AvroCellEncoder require the column URI from the CellSpec.
- AvroCellEncoder registers writer schemas on demand (DEVELOPER mode).
- Adds unit-test for developer validation.

issue: https://jira.kiji.org/browse/SCHEMA-530
review: https://review.kiji.org/r/989
KijiSchema API for Level 1 security.