new igalib.py - compute_bezier_extraction_1d()
new plot_nurbs.py - basic NURBS plots

- new _get_knots_tuple(), plot_parametric_mesh(), plot_control_mesh(),
  plot_iso_lines()
new eval_bernstein_basis()
move _get_knots_tuple() to igalib.py
new compute_bezier_extraction()
fix docstring
new get_raveled_index()
new tensor_product()
new combine_bezier_extraction()
new create_connectivity_1d(), create_connectivity()
update create_connectivity_1d() for both NURBS and Bezier bases

- fix for general knots
update create_connectivity() for both NURBS and Bezier bases
new compute_bezier_control()
fix docstrings
new get_unraveled_indices()
new eval_nurbs_basis_tp()
new plot_nurbs_basis_1d()
fix compute_bezier_extraction_1d() for knot multiplicity equal to degree
new eval_variable_in_qp()
fix 2D and 3D basis ordering in eval_nurbs_basis_tp()