from __future__ import absolute_import
mv root_collections to collection
mv math.physics.vector to vector
mv math.physics.measure to measure
rm math.physics
mv math.linalg.matrix to matrix
mv fit to stats
mv correlation.py and qqplot.py to stats/utils
new plot_quantiles example
fix tests
matrix improvements
fit.txt -> stats.txt
add matrices to class registry
add test for correlated_values
travis: install uncertainties and skip test if uncertainties cannot be imported