Deamonize clockwork

You are able to deamonize a clockwork process with -d using `deamons gem` and take advantage of daemons features like monitor, start, stop , reload etc

`daemons gem` is not required for `clockwork` to work and it is not specified as a dependency.  
It is only used if -d is specified.

`daemons gem` has to be installed thru `gem install` or specified in the `Gemfile` of the host project