It would be really handy to have `math:hash` that could be used as an operator

If we just rearranged the arguments, math:hash could be used as an operator. Put the string-to-be-hashed first, so that it is operated upon.

For example, instead of having to write:

      source_krl = http:get(url){"content"}
      source_hash = math:hash("sha256",source_krl)

we could use this one-liner:

      source_hash = http:get(url){"content"}.math:hash("sha256")

Granted, the current code could be written as a one-liner:

      source_hash = math:hash("sha256",http:get(url){"content"})

But that has to be read inside-out, which is not as convenient as the operator notation.

Start by reading the existing math:hash documentation and the KRL examples in the issue, then locate the parser or expression handling for operator notation in the pico-engine. Done means the string-first math:hash form works with the shown http:get(url){"content"} example while the existing function form remains supported.