Add support for \operatorname.
Add support for \DeclareMathOperator macros.
Ignore an \hline at end of array row.

We can't represent it yet, but we don't have to crash.
Closes #19.
Changed types of some symbols to fix spacing bugs.

- Added @ as ordinary symbol.
- Made . ? : \ ordinary symbols, not punctuation (see TexBook
  132-4,438).
- Added \colon as punctuation.

Thanks to Tomi Belan.  Closes #24.
Pandoc renderer: Don't put thinspace after Operators.

This often comes before super/subscripts, which looks bad.
See #24.
Made : Rel, not Ord.  (See #24.)
Support \providecommand (closes #15).
Merge pull request #17 from rekka/operatorname

Implementation of \operatorname and \DeclareMathOperator
Fixed bareSubSup so last merge doesn't break.
Insert braces around macro expansions.  Closes #7.

Previously applying macros could break expressions:
\newcommand{\vecx}{a + b}
$\hat\vecx$ --> $\hata+b$
Version bump to 0.6.6.
Added chagelog.
Changed data-files to extra-source-files.