High and Low init

[oscbyspro]

From oscbyspro/Numberick#7

There are two High and Low initializers at this moment:

init(ascending:  (low:  Low,  high: High))
init(descending: (high: High, low:  Low ))

While they are the most flexible options, they are also the least legible because they require 4 parentheses and sometimes an alias. I think that's a bit much, so I will add 4 briefer ones in order to alleviate my tuple-fatigue.

init(high: High)
init(low:  Low )
init(high: High, low:  Low )
init(low:  Low,  high: High)