Update with new functions

matlib 0.5.1

• added len() convenience function for Euclidean lengths
• added plotEqn3d() function using rgl to plot equations in 3 unknowns
• reorganized matlib.R to become a package .Rd document
• renamed proj() -> Proj() to avoid conflict with stats::proj()
• added vectors() for plotting geometric diagrams
• added vignettes/linear-equations