
Creates a 3-button widget that adjusts a floating point value.

fltk:Fl_Adjuster(x_position,y_position,width,height,"text label")

If height is greater than width, adjuster buttons will be stacked vertically.

When you press a button and drag to the right, or click a button, the value
increases.  When you drag to the left, or hold Shift or Ctrl while clicking,
it decreases.  The largest button adjusts by 100 * step(), the next by
10 * step(), and the smallest button by step().  Clicking on the buttons
increments by 10 times the amount dragging by a pixel does. Shift + click
decrements by 10 times the amount.

