Some incrementation funcs

incrementors.red

Red [
	Original-idea: "Dave Andersen"
	Source: https://gitter.im/red/red?at=5a2a4fb9a2be46682876463d
]
inc: func ['val][set val (get val) + 1]
dec: func ['val][set val (get val) - 1]
incr: func ['val step][set val (get val) + step]
decr: func ['val step][set val (get val) - step]
++: make op! :incr
--: make op! :decr
increment: func ['val /by step][set val (get val) + any [step 1]]
decrement: func ['val /by step][set val (get val) - any [step 1]]