Remove getKeySerDe(), getEntitySerDe(), and getEntityMapper() methods from
Dao since they are not a part of the public API.
Move KeyEntity to top-level class.
Remove public Dao#getScanner() methods that take a ScanModifier, since
the latter depends on the HBase API.
Remove Dao#getScannerBuilder() from public API since it has HBase-specific
Scan and Filter references. We can add a builder API back later if needed.
Move public API classes into com.cloudera.cdk.data.dao package. This is
not necessarily the final name, it was chosen just to group the API classes
together and may change later.
Group HBase javadoc
Reduce package visibility and move non-public Avro classes into an impl
package so they are hidden.

The only public packages are com.cloudera.cdk.data.hbase.{avro,manager,tool}.
Merge pull request #2 from tomwhite/CDK-112-hbase-api

Define HBase module public API and adjust visibility accordingly