Introducing new filtering architecture.

[Eugene Syromiatnikov]

On Sun, Jun 04, 2017 at 01:15:05PM +0700, Nikolay Marchuk wrote:
> Hello,
> This message describes new filtering architecture. Please, review it and
> give me feedback.

One more aspect which I forgot to cover: by which means you expect
to provide backwards compatibility for the existing filtering syntax.
I suggest drop the existing filtering code completely and convert
the expressions set by the current option syntax to the equivalent
filter expression at the option parsing time. What do you think about it?