Support mongoDb replica sets and local mongo _id

Use URIParser to create connections so that connections to either a
single mongo db or a replica set are supported. A replica set connection
is required in order to be able to keep inserting documents in the
replica set when the master fails over.

Add an option to automatically generate a mongo _id field using the
event timestamp when inserting a document.
Allow repeating a field in the hash config . Fix LOGSTASH-919
Allow empty arrays as values in grammar
range filter
some doc changes
rough first draft of metaevent filter
checkpoint
working proof of concept
fixed tag adding
field_remove option in base filter + fields are arrays only if they have more than one value
s/min/max/ typo
filter based on field names too + any or all match logic
statsd don't send event which are older than specified number of seconds
TyPo
Create cipher.rb

Adding a new filter. Cipher goal is to provide on the fly event content encryption and decryption. Beware of CPU cost.
New filter plugin "Advisor"
some docs changes
include & exclude keys parsed by kv filter
default_keys
fixed copy paste doc