[priority] parse `3x/5` as `3x / 5` instead of `3 x/5`

[evykassirer]

Parse 3x/5 as 3x / 5 instead of 3 x/5. It makes more sense to me and is what mathjs doe (pretty sure).

Spacing matters though - 3 x/5 should stay a multiplication between a 3 and x/5. I think this applies to any implicit multiplication? e.g. (2x+3)(3x+5)/2x would be (2x+3)(3x+5) / 2x - but we didn't decide on that earlier so feel free to debate that.

Aside: this was an interesting thing to me because I wonder how a brain interprets 3x/5 when it reads it. The way it's parsed affects how it's displayed to the user as well as the mathsteps algorithm so it really is part of the teaching too. I wonder how most brains interpret 3x/5? My guess is 3x / 5 though.

[evykassirer]

by the way, this is a priority for me because it's breaking some things in the porting process and it's hard to know how many of the remaining failing tests are because of this (though I'll eventually investigate further in mathsteps if this can't get done soon)

If you think it's straightforward to implement I could take a crack at it too if you don't have time - but if you do have time this would be the most helpful of all the issues I've opened!

[evykassirer]

ok not a priority anymore - I got around it by adding extra parens in the tests

but once it's done we can clean that up :)