Revert "TeXMath writer:  don't double up braces."

This reverts commit 89689e5b587a7ba7847b258901c60149c5238c17.
More small improvements towards release

1. Removed as many spaces as possible after commands
2. Improved handling of brackets
3. Improved handling of unicode text characters
4. Rejigging interface to Text.TeXMath.Writers.TeXMath to
   expose three functions, one which renders using the default packages
   one which renders with a specified package list and one which can add
the
   correct LaTeX environment afterwards.

I have tested that with these changes all the examples are still
compile with pdflatex.
Updated executables and tests