replaced vector and matrix of boost/ublas by VectorXd and MatrixXd of
Eigen library; improved computation of inverse matrix; adapted tests
Merge branch 'master' of
https://github.com/regiomontanus/FastPortfolioOptimizer.git

Conflicts:
	src/examples/example_runner.cpp
	src/optimizer/EfficientPortfolioCore.cpp
	src/optimizer/EfficientPortfolioCore.h
	src/tests/optimizer/EfficientPortfolioCoreTest.cpp
	src/tests/optimizer/EfficientPortfolioCoreTest.h