Initial import of xtrkcad version 1:4.0.2-2

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+This subdirectory contains a general character-set conversion
+library, used in Timber, and available for use in other software if
+it should happen to be useful.
+
+I intend to use this same library in other programs at some future
+date. (A cut-down version of it is already in use in some ports of
+PuTTY.) It is therefore a _strong_ design goal that this library
+should remain perfectly general, and not tied to particulars of
+Timber. It must not reference any code outside its own subdirectory;
+it should not have Timber-specific helper routines added to it
+unless they can be documented in a general manner which might make
+them useful in other circumstances as well.
+
+There are some multibyte character encodings which this library does
+not currently support. Those that I know of are:
+
+ - Johab. There is no reason why we _shouldn't_ support this, but it
+   wasn't immediately necessary at the time I did the initial
+   coding. If anyone needs it, it shouldn't be too hard. The Unicode
+   mapping table for the encoding is available at
+   http://www.unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/KSC/JOHAB.TXT
+
+ - ISO-2022-JP-1 (RFC 2237), and ISO-2022-JP-2 (RFC 1554). These
+   should be even easier if required - we already have the ISO 2022
+   machinery in place, and support all the underlying character
+   sets.
+
+ - ISO-2022-CN and ISO-2022-CN-EXT (RFC 1922). These are a little tricky
+   as they allow use of both GB2312 (simplified Chinese) and CNS 11643
+   (traditional Chinese), so we may need some way to specify which to
+   prefer.
+
+ - The Hong Kong (HKSCS) extension to Big5. Again, mapping tables
+   are available in the Unihan database.
+
+ - Other Big Five extensions, which I don't have mapping tables for
+   at all.