Added two new methods - LINESLOPE and LINEINTERCEPT

  1. LINESLOPE
  Returns the slope of the line joining (#1,#2) and (#3,#4) as a fraction = #5/#6

  2. LINEINTERCEPT
  Returns the intercept when y-a/x-b = m is reduced. Again, as a fraction
Compiling mobile.black.png at double the resolution