Add table-style filter utility

[arlimus]

This adds a new filter utility inspired by Stephan's filter_array. It is much more complex, however, as it aims to:

• only filter on known fields, not unknown ones
• fields in the source map can be strings or symbols
• optimized for printing the filtering chain
• can act on any type of field, including nil
• extend the owner class with accessor methods for this filter
• can retrieve entries as an embedded object with easy accessors to all fields

WIP: This is wip and discussions are highly welcome!

[vjeffrey]

read through it a couple times, I'm thumbs up - the tests helped me understand the intent of the code - makes sense!

[chris-rock]

I'd like to add an example using the inspec shell

inspec> xinetd_conf.services
=> ["time", "chargen", "daytime", "echo", "discard"]
inspec> xinetd_conf.where { service == 'echo' }
=> Xinetd config /etc/xinetd.conf with service == "echo"
inspec> xinetd_conf.where { service == 'echo' }.params
=> [{"disable"=>"yes", "type"=>"INTERNAL", "id"=>"echo-dgram", "socket_type"=>"dgram", "protocol"=>"udp", "user"=>"root", "wait"=>"yes", "service"=>"echo"}]
inspec> xinetd_conf.socket_types
=> ["dgram", "dgram", "dgram", "dgram", "dgram"]
inspec> xinetd_conf.where { socket_type == 'dgram' }
=> Xinetd config /etc/xinetd.conf with socket_type == "dgram"
inspec> xinetd_conf.where { socket_type == 'dgram' }.params
=> [{"disable"=>"yes", "type"=>"INTERNAL", "id"=>"time-dgram", "socket_type"=>"dgram", "protocol"=>"udp", "user"=>"root", "wait"=>"yes", "service"=>"time"},
 {"disable"=>"yes", "type"=>"INTERNAL", "id"=>"chargen-dgram", "socket_type"=>"dgram", "protocol"=>"udp", "user"=>"root", "wait"=>"yes", "service"=>"chargen"},
 {"disable"=>"yes", "type"=>"INTERNAL", "id"=>"daytime-dgram", "socket_type"=>"dgram", "protocol"=>"udp", "user"=>"root", "wait"=>"yes", "service"=>"daytime"},
 {"disable"=>"yes", "type"=>"INTERNAL", "id"=>"echo-dgram", "socket_type"=>"dgram", "protocol"=>"udp", "user"=>"root", "wait"=>"yes", "service"=>"echo"},
 {"disable"=>"yes", "type"=>"INTERNAL", "id"=>"discard-dgram", "socket_type"=>"dgram", "protocol"=>"udp", "user"=>"root", "wait"=>"yes", "service"=>"discard"}]