Add basic logging

# Addressing Issues #7 

I added a basic logging module which makes it easy to use the logging functionality within the project. I followed [this approach](http://stackoverflow.com/a/6768164/583592) as it seems interesting yet satisfying for my needs.

The way we'd use this logger depends if we're working with a *class* or a *module*.

## Class
```
module GitStatistics
  class Collector
    include Logging  # Add this so the class gets logging capabilities

    def method
      ...
      logging.info "Info Log Statement"    
    end  
  end
end
```

## Module
```
module GitStatistics
  module Utilities
    extend Logging  # Add this so the module gets logging capabilities

    def self.method
      ...
      logging.info "Info Log Statement"    
    end  
  end
end
```