Renamed some TextTypes to match order UnicodeData.txt.
Added beginning of tool to create toUnicode from UnicodeData.txt.
ToUnicode:  Use more complete tables generated by mkUnicodeTable.

There are some test failures to process.  I need to go through them,
but so far they all look like improvements.
Fixed bug in mkUnicodeTable; added Makefile.
TeXMath writer:  Don't emit empty \mathrm{}.
mkUnicodeTable:  Add comments showing characters.

This helps us see that the table is correct.
mkUnicodeTable:  Arrange map so that MATHEMATICAL entries are preferred.

(in cases where there are two possible renderings, e.g. a text
and a mathematical double-struck)
Updated tests.
Added lib/tounicode/Makefile to extra-source-files.

The Makefile is a nice form of runnable documentation about
build procedures.
MathML Reader: Now uses EDelimited to match braces
TeXMath Writer: EStretchy is reinterpreted as \\middle

This might need some tweaking and changes to other writers.
Added types to remove Stretchy from AST
Changes to remove stretchy