Updates pieces of the code that used "char" and assumed it was signed to use "sbyte" instead.
Adds "-funsigned-char" to the base compiler flags to really ensure the code base is free of assumptions and to further ensure it is interoperable with other toolchains that use "-funsigned-char".
Adds a note to the style guide.
Tweaks the drdecode_x86 test to fail without the fixes here in the x86 decoder.
Fixes #1034 (closed)