Ddf-utils

- add ddfSchema creation to datapackage
- bug fix and improvements

- bug fix in datapackage generation

- performance improvement on datapackage generation
- add progress bar to datapackage generation

- bug fix in ddfSchema generation

- the chef_new module, which is to replace the chef module. But it's still WIP, not working yet.
- ddf_utils.index renamed to ddf_utils.datapackage
- new interface for DDF Dataset and Datapackage
- removed python 3.3 support, because it's not supported by latest pandas now
- add support for ddfSchema creation
- bug fix for procedures/functions
- minor improvments

- new subcommands for `ddf`: `diff` for comparing 2 datasets
- DDF() now accepts absolute path to datasets