Bangle.js 2 Cutting Edge - new heart rate algorithm

Maybe the FLOAT_ABI_HARD won't be needed for all espruino code.

It seems hard to mix, but if you can find a solution I'm open to it - in a way I'd prefer not to change.

But it is only for Bangle.js 2 - I've kept everything else as softfp to avoid things getting broken.

But I did a quick test with:

function m() {
  for (y=0;y<32;y++) {
    line="";
    for (x=0;x<32;x++) {
      var Xr=0;
      var Xi=0;
      var Cr=(4.0*x/32)-2.0;
      var Ci=(4.0*y/32)-2.0;
      var i=0;
      while ((i<8) && ((Xr*Xr+Xi*Xi)<4)) {
        var t=Xr*Xr - Xi*Xi + Cr;
        Xi=2*Xr*Xi+Ci;
        Xr=t;
        i++;
      }
      if (i&1)
	  line += "*";
      else
          line += " ";
     }
   //  print(line);
  }
}

t=getTime();m();print(getTime()-t);

And as far as I can tell, hardfp is faster - maybe 5.5s vs 5.7s so not a lot, but it's noticeable and reproducible. Seems a shame to have everything running slower just for the extremely rare case of floats + inline C that I'd argue literally only you currently uses (and you make your own builds anyway!)