Fix multi-byte character handling.

Must divide by 256, or 0x100, since each byte has value [0 - 255],
[256 - 511], etc. so every time the code point increases by 256 it means
one more byte is used. Dividing by 255 causes problems for zip files
that contain 255 as an actual code point but it is not unicode
(multibyte).
Add regression unit test for previous fix.
Merge pull request #9 from WhiteHalmos/master

Fix multi-byte bug introduced in 7b1a4f