[CS2] May offer an compile option use let instead of var

[IamIpanda]

I have read the paragraph let and const: block-scoped and reassignment-protected variables on the coffeescript v2 website, But I want:
May you offer an option, make coffeescript ALL USE let instead of var in compiled code as it's also only one type of variable. Using var sometimes trouble me like in the code under:

fs = []
a = [1,2,3,4,5]
for i in a
	fs.push -> console.log i
f.call this for f in fs

If I'm asking for a selection whose conclusion had been made, I'm sorry and just close this.

[GeoffreyBooth]

Duplicate of #4255.