Changed algorithm to speed up fixSingleBitErrors() and fixTwoBitsErrors().

Old: Modify a single or two bits in a message, recalculate CRC,  start over until a CRC error free message is found.
New: Calculate CRC, identify incorrect message bits, correct message.

* The new approach does not need to recalculate the CRC of the whole message for each iteration. Allows fixing of two bit errors on "slow" systems like RaspberryPi.
* DF11 and DF17 messages are subjected to TwoBitErrorCorrection if '--aggressive' is used.