OMML: Reader unqualify TeXMath types

We don't have to worry about collisions anymore.
First stab at intepreting string types.
OMML: improve grouping.
Move Exp-processing functions to Shared.

These aren't specific to MathML.
Fix one more String-processing part.
Add fixTree to OMML.
Fix Groupings in Delims.
Fix TextType error.
Merge pull request #60 from jkr/cleanup

OMML fixes.
OMML reader:  Heuristic for distinguishing EText/EIdentifer.

This is not 100% accurate, but it's better than before.
OMML: Improved handling of unicode spaces.

I notice a lot of code duplication.  I'll work on creating
a central mapping of unicode spaces to widths that can be
used in all the writers/readers.
Shared: Export getSpaceWidth, getSpaceChars.

Use this in OMML reader.  TODO: other readers, writers.
Use Rational instead of Double in ESpaced, EScaled.

This should eliminate rounding errors in round-tripping.
Further moves towards using rationals for spaces.
Improved spacing.

Use ESpace rather than EText when a mathml mtext just contains
a space.

Use \mspace when needed to get latex spaces with odd sizes, rather
than finding the closest simple command.

Fixed some small errors.
TeX writer: Use \genfrac for \brace, \brack, etc when amsmath available.
Updated README with OMML reader.
Updated authors in man page.
TeX reader: handle \genfrac.
Properly escape { in \genfrac. Added genfrac tests.