BigInt_from_hex_string requires its parameter to have full words

[wjmelements]

For a word size of 8, I would expect BigInt_from_hex_string(2, result, "abcdefABCDEF0123456789" to make [abcdef, abcdef0123456789]; instead it makes [0,abcdef0123456789]. It works if you pass "0000000000abcdefABCDEF0123456789".

This is consistent with the behavior of BigInt_to_hex_string though, which pads zeroes.

My main complaint is that I would expect the parsing function to not require its parameters to be padded to the word size. I don't use this function much outside testing though, so it's not too important for my use case.