Issue 27: Fixed.
Issue 27: Fixed.

The 4 arithmetic operators were re-named and one was unified according to the agreement in Issue 27.

e-B51 HEAVY PLUS -> HEAVY PLUS SIGN
e-B54 HEAVY DIVISION -> HEAVY DIVISION SIGN
e-B52 HEAVY MINUS -> HEAVY MINUS SIGN
e-B53 HEAVY TIMES -> HEAVY MULTIPLICATION X (unified with U+2716)


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