`scipy` is Now Optional for Dense Matrices

• scipy is now optional for the dense matrix solver. By default PyNite uses the sparse matrix solver. If you wish to use the dense matrix solver, you'll need to set the sparse parameter equal to False when you analyze a model. Generally, the sparse matrix solver is faster and uses less memory. This feature was added to improve compatibility with other programs that may not work well with scipy.
• Started work on a Renderer class for visualization to better organize the code.
• Renamed several variables in the render_model function to make them more descriptive of what they control. If you use keyword arguments in your calls to render_model you may need to change some of the variable names.