Merge some of update by document and script

These share many of the same options so it makes sense to merge them.
This also adds support for things like _retry_on_conflict and _routing to
updates by scripts.

Closes #628
Closes #627

Author: Nik Everett

changes.txt

@@ -3,6 +3,7 @@ CHANGES
 2014-06-13
 - Stop ClientTest->testDeleteIdsIdxStringTypeString from failing 1/3 of the time #634
 - Stop ScanAndScrollTest->testQuerySizeOverride from failing frequently for no reason #635
+- rework Document and Script so they can share some infrastructure allowing scripts to specify things like _retry_on_conflict and _routing #629
 
 2014-06-11
 - Allow bulk API deletes to be routed #631