TeXMath Writer: EStretchy is reinterpreted as \\middle

This might need some tweaking and changes to other writers.
MathML Reader: Now uses EDelimited to match braces
Various: Removing EStretchy from source
TeXMath reader:  removed undefined in Delimited, added 'fence' helper.
Removed EStretchy from Types.
TeXMath Writer: Improved delimiter rendering
Merge pull request #46 from mpickering/master

Improved diacritical mapping and correct matrix environments
TeXMath writer: Avoid pmatrix* etc.

They require the mathtools package.  Instead, use regular
array environment when we don't have all centered columns.
Updated tests for d*dot changes.
Merge branch 'delimited' of https://github.com/mpickering/texmath into mpickering-delimited

Conflicts:
	src/Text/TeXMath/Writers/TeXMath.hs
Merge branch 'mpickering-delimited'
Updated tests.
Tests: Fixed StretchVert1 test
MathML Parser: Improved parenthesis matching
Merge pull request #48 from mpickering/delimited

Improved parenthesis matching
Updated tests for PR #48.
MathML Writer: Added position information to fences