Added support for different size of TX and RX buffer sizes.
Added support for buffer sizes bigger than 256 bytes.
Added possibility to overrule the default size.

Added support for different size of TX and RX buffer sizes.
The default values remain the same. You can however specify a different
value for TX and RX buffer

Added possibility to overrule the default size.
If you want to have different values
define SERIAL_TX_BUFFER_SIZE and SERIAL_RX_BUFFER_SIZE on the command
line


Added support for buffer sizes bigger than 256 bytes.
Because of the possibility to change the size of the buffer sizes longer
than 256 must be supported.
The type of the indexes is decided upon the size of the buffers. So
there is no increase in program/data size when the buffers are smaller
than 257