Arrows coloured differently for pos&neg

black for positive and red for negative
initial equation width setup

gridlines changed on numberline.
double-arrow displaying correctly

Also detects click collision. Display still not working for stepCount>0
running changes

nothing significant changed
arrows now space to text width

not perfect, but a start. Need to pull grid lines out of number line
method and also work out how to deal with the double-arrow spacing.
moved guide lines code

now in main draw statement rather than drawStep method
interim commit

still trying to make arrow spacing work
start change to reference point

briefly (hopefully) not working
spacing cleaned up from arrow reference point

still some issues with dimensions of final horizontal black line.
keypress delete works

delete or backspace deletes previous step
arrow formation now bounded

User cannot form arrows beyond the range min to max.
vertical jitters fixed
Merge pull request #2 from Cheddles/arrowSpacing

Arrow spacing