Merge pull request #3 from mikea/sgradient

Stochastic Gradient Optimization
Ignoring sublime files.
Simple sgrad benchmark
Renamed V64 vector type to F64
Introduced vector.B for boolean vectors.
Array helper functions
Introduced MatFile object
Logistic Regression binary classifier.
Small API improvements
Catching up on other refactorings.
pgm7 logistic regression example