FEAT: transparent round/to x 0

[hiiamboris]

Following the discussion ☝️ April 22, 2021 9:27 PM and TG chat.

Summary

Rationale: to not create special cases where they aren't required

Example:

>> round/to pi 1
== 3
>> round/to pi 1e-10
== 3.1415926536
>> round/to pi 1e-100
== 3.141592653589793
>> round/to pi 1e-500
*** Math Error: math or number overflow
>> round/to pi 0
*** Math Error: math or number overflow

As scale approaches zero we should expect the result to come closer and closer to the original value.
With the lim (round/to value scale) = value when scale -> 0.
The zero can be reached in practice as mentioned in the above discussion, so it makes sense to handle it automatically, leaving programmer with less headaches.

This PR implements x = round/to x 0 invariant, even for special floats:

>> round/to pi 0
== 3.141592653589793
>> round/to now/time 0
== 21:10:46
>> round/to 1.#inf 0
== 1.#INF
>> round/to -1.#inf 0
== -1.#INF
>> round/to 1.#nan 0
== 1.#NaN

[dockimbel]

This PR is changing the meaning of the /to refinement for round. The current meaning is:

REFINEMENTS:
     /to          => Return the nearest multiple of the scale parameter.
        scale        [number! money! time!] "Must be a non-zero value."

This PR should at least update the doc string accordingly.

[hiiamboris]

Thanks! Fixed!

n [number! money! time! pair!]
/to "Return the nearest multiple of the scale parameter"
scale [number! money! time!] "If zero, returns N unchanged"

[greggirwin]

All OK by me.

[dockimbel]

@qtxie Are you OK with the changes made by this PR?

[qtxie]

@dockimbel Yes. I'm OK.