HBASE-8693 Extensible data types API

WIP. This patch introduces an extensible data types API for HBase. It
is inspired by the following systems:

 - PostgreSQL. Postgres has a user-extensible data type API, which has
   been used to great effect by it's user community (ie, PostGIS). The
   desire is for HBase to expose an equally extensible data type API.
   One aspect of the Postgres data type is the ability to provide
   equivalence functions for index operations. This appears to be of
   critical performance utility for its execution engine.
 - Orderly. Orderly handles the issue of compound rowkeys by providing
   convenience classes for handling these kinds of data types. This
   influence is reflected in the Struct and Union family of classes.
 - Phoenix. The PDataType enum used in Phoenix provides type hints,
   similar Postgres's equivalence functions. These appear to be used
   during query execution for numerical type promotion.

This patch is intended to exercise the OrderedBytes API, particularly
around numerical value support. The other intention is to establish
the set of data types HBase should provide out of the box. This list
is becoming quite sizable and includes both the "standard" types as
well as "legacy" types to help developers transition their existing
applications. The final intention of this patch is to shop around the
data types and API for their definition with a wider audience. It does
not address the type compatibility concerns expressed by Phoenix's
PDataType API (ie, isComparableTo, isCoercibleTo); these will be
address in a different JIRA.
expose LegacyBytes's additional read/write methods
HBASE-8693 [example] Use DataType API to build regionNames

This is an example of using the HDataType classes to manage
HRegionInfo's regionName. It could probably be taken a step further to
manage the MD5Hash as a LegacyBytesFixedLength, then the size of the
allocated buffer could be calculated with
HREGIONINFO_NEW_CODEC$encodedLength() instead of by hand.
HBASE-8693 [example] KijiFormattedEntityId

Demonstrates using HDataType to implement kiji-schema's rowkey
concept, FormattedEntityId.