Added EStyled to Exp, implemented in all readers and writers.

EStyled corresponds to mstyle in mathml, and \mathrm, \mathcal, etc.
in LaTeX (which can contain arbitrary math content, not just text).

Note that the Pandoc writer now uses toUnicode to support things
like mathfrak.

Test suite: Split native files before diffing.

Tests not yet updated.

Closes #13.
Merge branch 'master' of https://github.com/mpickering/texmath into mpickering-master

Conflicts:
	src/Text/TeXMath/Readers/MathML.hs
	src/Text/TeXMath/Writers/OMML.hs
	src/Text/TeXMath/Writers/Pandoc.hs
MathML reader: Handle different math space attribute values.
Regenerated tests.

They need to be checked again, of course!
TeXMath writer:  for EText use getTeXMath instead of unicode.
TeXMath reader:  properly add default alignments in array/matrix.

Previously we just got [] for default alignments, which
caused problems in latex output.
TeXMath reader:  refactored handling of default alignments.
TeXMath writer: properly handle cases environment.
TeXMath reader: handle matrix, smallmatrix.
TeXMath writer:  only use ams matrix environments if amsmath in env.
TeXMath Writer: Fixed regression in bracket matching
TeXMath Writer: Improved matching of brackets deep in the structure