Feature: add silence_record_build option

effectively allows listen to report existing files as an add event so
that the same treatment can be applied to existing and newly added
files.

Note that while it seems to work well when I fold it into some test code and my non-acceptance tests pass ok, I am unable to get my acceptance test to work... (https://github.com/hackify/listen/blob/master/spec/acceptance/listen_spec.rb#L188)

I created this because I am building a ruby port of my Node.js module for hackify.org (https://github.com/hackify/hackify).  The node module I use for listening to the file system (https://github.com/paulmillr/chokidar) supports this feature.

The feature is useful for this application because I need to do an initial listing of files in my 'watched' folder as well as report differences.  Without this feature, I would need to have a separate function to recursively browse the folders and apply the ignore regex as well.  Pretty messy I thought.