That would certainly work as well, and ultimately it does get converted into a Vec<u8>. I did consider just having the buffer as it from the start, but by using a String it was just a little more intuitive when it came to pushing more bits onto the buffer, as well as doing the padding operation at the end. More just to reduce complexity during development than anything I guess.
I may have overlooked some things, but I made a quick PR[0] just to see what this would look like using a Vec<u8>. Feel free to close if you prefer the original.
