Serial conversion in c2p.library 1.7

c2p.library 1.7 uses a serial approach for convert chunky to 1, 2 and 3 bitplanes.

Using the ADDX instruction, we can implement the conversion bit per bit, using a relative smaller inner circle. For 4+ bitplanes, the old MEXG (masked AND + XOR register exchange) parallel approach is still faster.

Last but not least, major source code refactor, implementing a specific conversion method in each file, resulting easier to maintain.