Began exploration of continuous features

Added Continuous.fsx as a playground
Initial continuous variables functions

Split continuous features by MDL, and began writing code to integrate
with categorical features.
Renamed Branch to CatBranch

Began reorganizing tree, to separate categorical and numeric branches.
Script with unified float/int branches draft
Added Entropy and MDL modules

Moved Entropy related functions into Entropy module, with basic tests.
Added MDL module, untested.
Moved script Continuous into HybridTree
Fixed bug in MDL class count
Rough pure continuous variables tree working
Somewhat broken continuous variables tree

WIP: partially implemented growing tree on pure continuous variables,
something is not quite right and needs fixing.
Project upgrade for VS2013
Fixed ridiculously stupid bug

Features were filtered the opposite way from what should have been done.
Added mostLikely in continuous branch
Created records for Dataset and Branch data
Began integration of Numeric and Categorical
Indexes all use int[], categorical super slow
Fixed Index tests
Integrating different splits into tree
Messy hybrid tree working
Chainsaw time, probably broken
Improved extracting count from Seq

Entropy.countFrom extracts reasonably efficiently count of individual
instances from Seq of elements