Unified json library

The java project depends on several json libraries, can we unify them into one so that we can also reduce the dependencies.

use jackson-core in orc-benchmarks-core
org.apache.orc.bench.core.convert.json.JsonWriter

use gson in tools
org.apache.orc.tools.convert.JsonReader
org.apache.orc.tools.json.JsonSchemaFinder
org.apache.orc.tools.json.JsonShredder
org.apache.orc.tools.json.TestJsonSchemaFinder

use jettjson in tools
org.apache.orc.tools.KeyTool
org.apache.orc.tools.JsonFileDump
org.apache.orc.tools.PrintData

I could provide a pr to unify the json library. But I'd like to hear from people
1. is the unification necessary?
2. if so, which library do we use? jackson/gson/jettison