Add multi-target code
Initial multi-target commit.

Merges albert/moa repository with multi-target code developed by Albert
at Porto.
Add multi-target instances
Merge branch 'joaomaiaduarte-multitarg' into multitarget
Add multi-target tab
Update MultiTargetInstanceStream
Update ArffFileStream
Fixed bugs related with MultiLabel/SingleLabel representation (for
backward compatibility)
Prediction class for multilabel getVotes.
Initial draft for AMRules MultiLabel
Supporting classes AMRules Multilabel. General algorithm still not
implemented.
Adaptive multi-target regressor completed.
New package structure for multilabel rules.
Some other fixes and renaming (error measurers).
MultiLabel BSTrees completed.
Some MultiLabelAMRules bugs fixed
Fixed a bug in reading multilabel data streams.
Implemented VarianceThreshold output selector.
Two probability functions for anomaly detection added.
These were integrated with AnomalinessScore and used as option.
Nominal observer for multilabel instances.
MultiLabelAMRules - Added nominal attributes support for learning
literals.
Move method from LearningLiteralRegression to LearningLiteral
Move method from LearningLiteralRegression to LearningLiteral
Merge pull request #5 from joaomaiaduarte/multitarget

Multitarget update
Update Instances