int_to_bin assumes signed integer when converting to bytes

[Nambarc]

Problem was found when encoding a dictionary back into a NMEA message.

In the int_to_bin function in the util.py file, the second to last statement converts the value into bytes and then into a bit array. However, when the value is converted to_bytes it always assumes the value is signed.

I ran into an issue when encoding a message type 5 that had a draught value of 12.8. 12.8 gets multiplied up to 128 in the from_course function. 128 is then ultimately passed to int_to_bin and expected to fit into 1 byte. However, a signed value of 128 doesn't fit into 1 byte. So I think int_to_bin needs to be told the signed-ness of the value from the calling function, it can't always be set to signed=True.

[M0r13n]

Hey @Nambarc,

thanks for bringing this up. You are right. This will be fixed with #61 and will be available in the next release.