DDLSHELL-15. kiji-schema-shell supports formatted row keys.

Signed-off-by: Christophe Taton <taton@wibidata.com>
DDLSHELL-17. Improve default top-level error message.

Signed-off-by: Lee Sheng <lsheng@wibidata.com>
DDLSHELL-22. Make HASH PREFIXED(2) the default key format.

If the user doesn't specify a key format, use a single hash-prefixed
string key component. The hash prefix is 2 bytes of the MD5 sum of
the key.

The previous default was to persist the 16-byte MD5 hash of the key,
and drop the key's plaintext entirely.
DDLSHELL-21. Refuse to edit newer layouts.

Require the table's layout version to be <= the max version
supported by this instance of the tool.