add size parameter to conversion methods

See https://bugs.launchpad.net/intelhex/+bug/372625 for reference.

sneakypete wrote:

To give a quick example:
    for addr in range(0, EEPROM_SIZE, BLOCK_SIZE):
        eeprom.i2c_write(addr, ih.tobinarray(addr, addr + BLOCK_SIZE - 1))

The "-1" is messy, and shouldn't be required (and looks a lot like visual basic!).

I agree, it's messy. We can provide a better API (without API break) by introducing additional size parameter. So the example above will be:

      for addr in range(0, EEPROM_SIZE, BLOCK_SIZE):
          eeprom.i2c_write(addr, ih.tobinarray(start=addr,
                                               size=BLOCK_SIZE))

I think it's more readable.

To avoid API break this new parameter should be added after existing ones, e.g. method signature should be:

    def tobinarray(self, start=None, end=None, pad=None, size=None):

and we have to check that start is not None and end is None when size is not None.