Allow definition of an application setup file

In an effort to off-load as much intelligence as possible onto the 
application using eye-patch, a :setup_file option can be defined 
(relative to the working_dir) which will be required as part of eye's
config parsing.

This allows injection of methods/callbacks/what-have-you when eye is
starting up.
Add process before_spawn hook support

Specific applications may need to invoke specific behaviors prior to
spawning a new process, such as writing temporary information to a file 
descriptor.