Builtin functions: abs (fabs), ceil, floor, round?

[tclose]

I have a feeling that we have discussed this at some point but I can't remember what we decided if we did, are discontinuous functions such as abs (or fabs if we want to be fully C89 compliant), ceil, floor and round valid in 9ML? As they are not in the spec. abs could be implemented via a piecewise function (see #83) but would be a bit of a pain, and the others wouldn't be able to be.

Also, log10 is in the spec but probably doesn't need to be (although probably wouldn't hurt)