update contributing page
extend ES InputFormat for running under Hive operations/functions

add dedicated HiveESInputFormat to deal with scripts that use Hive
functions. As Hive through-out its code base assumes a File store (and
thus FileInputFormat and FileSplit), running without it causes all
sorts of weird exceptions.
HiveESInputFormat wraps ESInputFormat as a FileInputFormat while
preserving various Hive settings to make Hive work.

fix #59
minor cleanup