Added arithmetic test

All arithmetic operations (and the STOP command) are covered. Especially important is the SMOD command, due to the lack of an exact mathematical definition, every compiler handles it differently. For example a python compiler usually gives different results for the SMOD operation than a C compiler.
The ethereum/tests repo (branch develop) needs to be updated in order to get the vmArithmeticTest.json file.
sorry - that should be "0x"+toHex(toCompactBigEndian(_v))