Fixes classloader issues like those occur in sbt and ANT(issue #107)

This pull request aims to fix classloading issues with regard to the JRuby runtime using the classloader of the  current thread which in some cases( for instance in ANT or sbt) may not have all JRuby required classes and other dependencies on the classpath.

By adding a create method in which you can pass in the classloader to use these issues can be solved.