add some options and a few bugfixes

    - minor linter fixes (mostly trailing whitespaces)
    - new Processor options: showLines (show triangle lines), bgColor, color, viewerwidth, viewerheight
    - fix makeAbsoluteUrl to also deal with absolute paths
    - processor.setLineDisplay to set showLines option post-hoc
    - minor bugfix in createElements
    - propose to reverse rotating behaviour (alt key vs not) in mousemove - seems more natural