Add several spelling corrections

calcualte->calculate
calcualting->calculating
cooridnate->coordinate
consuder->consider
easer->easier, eraser, 
finnished->finished
lenth->length
nortmally->normally 
opproximate->approximate
ourselve->ourselves
reander->render 
shoild->should 
shouls->should 
similat->similar 
winn->win