Add cache logging support

[dblock]

Create a feature around cache logging. We want to see what Garner is reading or writing to/from cache with a single switch. Currently this monkey-patch:

module StoreEx
  def read(key, options = nil)
    puts "read: #{key}"
    super
  end

  def read_multi(*names)
    puts "read_multi: #{names}"
    super
  end

  def write(key, value, options = nil)
    puts "write: #{key} => #{value.class}"
    super
  end

  def fetch(name, options = nil)
    puts "fetch: #{name}"
    super
  end
end

Garner.config.cache.extend StoreEx