corrected error in cellProp[iCell].iRangOfMax and iAzimOfMax (no equivalent in Adriaans reference code)
added some more FIXMEs with equivalent lines in Adriaans reference code
    // FIXME *nzdata unused
added a couple of 'equivalent line' numbers for easier comparison with Adriaan's code later
replace vol2bird's dist method with a more robust method. Fixes issue #31. Updated the unit tests, needed slightly larger delta.