Merge pull request #54 from mpickering/master

MathML Reader: Improved handling of compound operators
Removed EBinary, added EFraction, FractionType.

None of the writer tests change except for a very minor different in
binomial coefficients in OMML and MathML.  So this change mostly affects
internals.
MathML reader:  convert from unicode characters in styled sections.

This helps get us closer to making writeMathML . readMathML an
identity, since writeMathML uses toUnicode.

Removed the fromUnicode from TeX writer, as it's no longer needed
there.
Fixed the \varepsilon and \epsilon mess.

* Switched the definitions in EntityMap (bizarrely, HTML has different
  mappings for these character names than MathML and LaTeX, as
  documented on the W3C page itself).
* Fixed the \varepsilon character in the TeX reader.
* Updated tests.
TeX writer:  Make sure we have {} after \phantom.
Updated changelog.
Fixed textual latex escapes.

Previously we were using some math-mode escapes in text-mode contexts.
TeX reader/writer: Support \choose, \brace, \brack, \bangle.

Added test case tests/src/choose.tex.
Closes #21.
Updated changelog.
TeX parser: rewrote without parsec's token parser.

This way it's simpler to see what is happening.
TeX reader: small parser tweaks.

Remove unneeded try.
TeXMath Reader: Improved error messages