added --tree-stats option to diff-tree
added py4j entry point
added export-diff op and shp wrapper
modified py4j entrypoint
Changed iterator used during import, so it can replace fid and feature type

That functionality had been mistakenly left aside after changes made to improve performance
extended ExportDiffOp to include feature ids in atributes
improved command parsing in py4j entry point, to allow using parameters with quotes
changed assembly task
changed fid field name to "geogit_fid"
changed tokenizer in py4j so it can accept parameters with endlines such as multi-line commit message