add explicit and assignment operator to DenseMatrix
add NewtonRaphson
add tests for NewtonRaphson
Declare and init vars in same place.
Add spaces around operators.
fix copyright
Merge pull request #31 from endJunction/add-Newton

Add newton
no need for static_cast
correct typo
Merge pull request #348 from norihiro-w/add-Newton

Add Newton-Raphson nonlinear solver