Function macro expansion bug when multi argument macro arg has same name as user input

[AndrewRayCode]

Reproduce

#define F(x, y) x + y
F(y, x)

gets expanded to

x + x

because the replacement of each argument is a separate string replacement pass. So first it replaces the first argument, x, with what the user supplied, y, making the string y + y. Then it goes on to replace the second argument, y, with the user supplied x, making the string x + x.

This bug is triggered when a function macro has more than one argument, and the second argument (in this case y also matches what the user replace the first argument with.

Fix

I switched the replacement to be a single pass replace, so there is no second pass to clobber the first replacement.

Addresses #31