Define `filter`

[andyferris]

I was searching through some data for a particular row and noticed that [row for row in json_table if pred(row)] is ridiculously fast (much faster than creating a DataFrame from it and then filtering).

It would be nice to be apply a row filter directly via filter(pred, json_table) like you can with a DataFrame or many other table types. Clearly it already supports Iterators.filter so why not Base.filter? :)