encoding: default ambiguous character to narrow The current implementation of colwidth was treating 'A'mbiguous characters as wide, which was incorrect in a non-East Asian context. As per http://unicode.org/reports/tr11/#Recommendations, we should instead default to 'narrow' if we don't know better. As character width is dependent on the particular font used and we have no idea what fonts are in use, this recommendation applies. This introduces HGENCODINGAMBIGUOUS to get the old behavior back.