Added support for truncation of objects, arrays, strings

Array entries, object properties and string length can be configured to
be truncated so the log output stays clean. By default no truncation takes place. 
Pay attention however: the truncation may hide logging elements you don't want to miss.
This feature is useful for us because we use eyes.js in combination with a winston logger to rewrite the meta object of log messages so it doesn't display endless arrays etc.