Add a new prededined function fileExists

The `fileExists` function will return true if the file exists, false if it doesn't.
The parameter is either a `java.lang.String`, a `java.io.File` or a `java.nio.file.Path`.
Thierry Chantier joins as a contributor
Merge pull request #67 from titimoby/new_function_fileExists

New prededined function fileExists
Attach assemblies

This will allow distributing Golo release images to Maven Central instead of Sourceforge.
Support for varargs in dynamic object methods
Merge pull request #68 from jponge/wip/fix-dynobj-varargs

Support for varargs in dynamic object methods