New aliases add & sub

[akarzim]

Here is a proposal. I'm not convinced by the .+() syntax, it doesn't seem natural to me. That's why I propose two aliases:

alias_method :add, :+ 
alias_method :sub, :- 

Usage:

irb(main):001:0> Date.today
=> #<Date: 2021-02-05 ((2459251j,0s,0n),+0s,2299161j)>
irb(main):002:0> TimeCalc.today.add(4, :days)
=> #<Date: 2021-02-09 ((2459255j,0s,0n),+0s,2299161j)>
irb(main):003:0> TimeCalc.today.sub(4, :days)
=> #<Date: 2021-02-01 ((2459247j,0s,0n),+0s,2299161j)>