Custom log provider

[chimurai]

Introduce option.logProvider

Ability to use a custom log provider, such as:

• winston
• log4js

Default logProvider uses console to do the logging.

option.logProvider = function (provider) {

   // override logger.error()
   provider.error = function (message) {
      // do something
   }

   return provider
}

Or complete replace the default log provider:

option.logProvider = function () {

   var provider = {
      log : console.log,
      debug : console.log,    // use .log(); console does not have .debug()
      info : console.info,
      warn : console.warn,
      error : console.error
   };

   return provider
}