[encoding] "gb18030 ranges" have problematic definitions (#17)

It seems that for some code points, gb18030 ranges doesn't
have a round-trip mapping.  Take the code point U+8000 for example.
  
When we apply the the "index gb18030 ranges pointer" we get:

    32768 ---> 18962, 0x4DAF --> 18962 + 32768 - 19887 --> 31843

but when we apply the "index gb18030 ranges code point" from
31843 we get:

    31843 ---> 19043, 0x9FA6 -->  40870 + 31843 - 19043 --> 53670

and that differs from our original 32768.  I think the reason is that each range is poorly defined; it's not clear where each range starts and ends in "index-gb18030-ranges.txt".

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/encoding/issues/17