Removed dependency on OpenCV, fixed bugs, crisper rendering and added 8 new commands.
Commands added:
* circle(radius, coord_list, brush=None)
* slice(radius, from_angle, to_angle, coord_list, brush=None)
* set_plot_font(plot_font)
* ask_plot_font()
* ask_paper()
* ask_pen()
* ask_brush()
* ask_charset()
Bug fixes:
* No longer draws everything one pixel higher
* More precise and faster rendering
* Cursor now matches pen colour
* Fixed wonky font images
* Fixed RM Nimbus logo image
* Fixed intermittent floppy drive
* Shutdown by CTRL-C interrupt doesn't get delayed