Added elasticsearch lua module and es_payload encoder to replace
`format = "payload"` config option from v0.5.2.
Have to explicitly put functions in our namespace when we override
the globals before we can use them, duh.
Newlines and whitespace.
Integrate review feedback: clarify windows time formatting, fix `ns`
variable scoping bug, save an allocation by avoiding a string.format
call.
More review tweaks: table lookup spelling, scope change, doc wording.
Merge pull request #890 from mozilla-services/es_bulkapi_lua_module

Added elasticsearch lua module and es_payload encoder to replace