Script Filter: Support providing a custom script as a filter

[kimchy]

A new filter, using the new script support (as used in custom_score and script fields). For example:

"filtered" : {
    "query" : {
        ...
    }, 
    "filter" : {
        "script" : {
            "script" : "doc['num1'].value > 1"
        }
    }
}

Custom parameters can also be provided for it:

"filtered" : {
    "query" : {
        ...
    }, 
    "filter" : {
        "script" : {
            "script" : "doc['num1'].value > param1"
            "params" : {
                "param1" : 5
            }
        }
    }
}

[kimchy]

Script Filter: Support providing a custom script as a filter, closed by c278603.