Better built-in support for URI query parsing

[pvdb]

Production use of ntail often requires filtering on URI query params, which at the moment isn't very well supported out of the box.

Given a log line with the following uri part of the request component:

/index?qux=blegga&foo=bar

Using the DSL, building a filter on any of the URI query params cannot be more sophisticated then:

-f "uri =~ /blegga/"

Unless you resort to something like:

-f "CGI::parse(URI::parse(uri).query)['qux'] == 'blegga'"

It would be much easier/nicer if ntail implemented this out-of-the-box, something along the lines of:

-f "uri_query_params['qux'] == 'blegga'"

The following StackOverflow post contains a number of viable alternatives for implementing this ntail feature:

http://stackoverflow.com/questions/2500462/how-to-extract-url-parameters-from-a-url-with-ruby-or-rails

/cc @jspc