add comparison filters and TimestampsFilter

This change adds the full suite of HBase comparison filters to asynchbase.  `KeyRegexpFilter` should be considered for deprecation / removal, as it is superseded by `RowFilter`/`RegexStringComparator`.  The integration tests pass against HBase 0.94.6-cdh4.3.0, but fail against 0.96.1-hadoop1 while executing the `DependentColumnFilter` tests in `TestIntegration` with the following stacktrace:

```JAVA
compareFilters(org.hbase.async.test.TestIntegration): java.io.IOException: Cannot set batch on a scan using a filter that returns true for filter.hasFilterRow
        at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2210)
        at org.apache.hadoop.hbase.ipc.RpcServer$Handler.run(RpcServer.java:1876)
Caused by: org.apache.hadoop.hbase.filter.IncompatibleFilterException: Cannot set batch on a scan using a filter that returns true for filter.hasFilterRow
        at org.apache.hadoop.hbase.client.Scan.setBatch(Scan.java:353)
        at org.apache.hadoop.hbase.protobuf.ProtobufUtil.toScan(ProtobufUtil.java:888)
        at org.apache.hadoop.hbase.regionserver.HRegionServer.scan(HRegionServer.java:2980)
        at org.apache.hadoop.hbase.protobuf.generated.ClientProtos$ClientService$2.callBlockingMethod(ClientProtos.java:26929)
        at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:2172)
```

My best guess is that this happens because `Scanner` always sets `max_num_kvs`.  Is there a way to disable this?