ENH: Add functionEntry '#calc' to dictionary

- handles basic operations, references to other dictionary entries
  (with '$name' syntax) and assorted mathematical functions:

      pi(), degToRad, radToDeg, asin, acos, atan, sin, cos, tan, log,
      log10, mag, atan2, pow

The basic syntax: #calc{ ... };

NOTE the trailing ';' is required for the primitiveEntry to be
properly defined.