Add support for multiple multi-byte encodings in the :mod:`XML parser
<xml.parsers.expat>`: "cp932", "cp949", "cp950", "Big5","EUC-JP", "GB2312",
"GBK", "johab", and "Shift_JIS". Add partial support (only BMP characters)
for multi-byte encodings "Big5-HKSCS", "EUC_JIS-2004", "EUC_JISX0213",
"Shift_JIS-2004", "Shift_JISX0213", "utf-8-sig" and non-standard aliases
like "UTF8" (without hyphen). The parser now raises :exc:`ValueError` for
known unsupported multi-byte encodings such us "ISO-2022-JP" or
"raw-unicode-escape" instead of failing later, when encounter non-ASCII
data.
