Enable configuration via consuming application

Configuration options can be passed in via a block 
on the end app. 

Options include:
- log_level: :info or :error, defaults to :info
- output_type: :file or :stdout, defaults to :file
- logger_path: relative directory for log file,
defaults to “log
- logger_file: log file name, defaults to “servme.log”
- ignore_file_types: array of file extensions to 
  ignore without error. will still return a match 
  if one has been defined. Defaults empty.
- ignore_paths: array of paths to ignore without 
  error. will still return a match if one has been 
  defined. Defaults empty.
- ignore_param_keys: params keys to ignore. Will 
  not be used to match the param collection.
Add logging

Logger class is singleton that can be instantiated 
via `Logger.instance` and contains methods to 
nicely and consistently format different types
of loggable events.
Create separate stub filter, remove logic from stubber

Stubber now only handles building stubs
StubFilter handles finding the correct stub for a 
given request.
Add public methods to list stubbed paths and responses

Useful for debugging
require new classes
Update specs to test new functionality.
Update Version to 0.3.0