Bug fixing and new options:

- Fix for ensembles' local predictions when order is used in tie break.
- Fix for duplicated model ids in models file.
- Adding new --node-threshold option to allow node limit in models.
- Adding new --model-attributes option pointing to a JSON file
  containing model attributes for model creation.
First version with multiple multi-label fields
Updating new version to 1.2.0
Adding the --multi-label-fields option info to docs
New tests for --multi-label-fields
Code review, pep8 and pylint changes
Removes executable flag in bigmler.py
Adding the running the tests section in docs
Bug fixing: datasets generated using --new-fields are not used in models
Bug fixing: headers order in some multiple multi-label fields' sources
Changing copyright date and adding test file
Transmitting --training-separator option to create source calls
Refactoring multi-labels and adding attributes options

- Refactoring all multi-label resource's function to store and
  read the multi-label associated labels and fields' variables
  in a user_metadata attribute of each created resource

- Adding --source-attribute, --ensemble-attribute,
  --evaluation-attribute  and --batch-prediction-attribute
  to point to JSON files where attributes for creation function
  calls are specified
Refactoring the main routine and other pep8 and pylint cleaning
Adding missing arguments file
Adding new --batch-prediction-tag to docs and HISTORY
Changing variable to constant in labels processing
Adding new option --balance to balance the classes evenly
Adding --weight-field option to weight each instance based on one field contents
Updating version to 1.4.0 and adding docs info for --balance and --weight-field