HBase Storage

Here's the start of an HBase storage module.  It's still in pretty early form but I wanted to get this up so that reviews could start early.


## Tables
* zipkin.traces
* zipkin.duration
* zipkin.idxService
* zipkin.idxServiceSpanName
* zipkin.idxServiceAnnotation
* zipkin.topAnnotations
* zipkin.dependencies
* zipkin.mappings
* zipkin.idGen

## Internals

I created a non-blocking futures based version of HBase's HTable.  This HBaseTable uses a thread pool to execute the calls to HBase.

Currently it's using HBase 0.94.9 and hadoop 1

## Row Keys Construction

Whenever possible I am using a fixed length row key.  That necessitates a set id for any variable length strings that can be on the row key.  This mapping is created using the mapping table and the id gen table. The idGen table holds the last idGenerated.

* There can be up to Long.MaxValue services
* Each service can have Long.MaxValue spanNames and annotations

The mapping table holds the mapping of Array[Byte] to id and the reverse.

## Still ToDo
* counters, counters, more counters
* Allow this to build against current hbase trunk