- Remove outdated comment
- Fix code block delimiter

Initial version of an XSLT stylesheet that converts the XML format
produced by `cmark -t xml` back to Commonmark.

Fixes #264

* Add test to illustrate issue

* Provide some test fixes

* Don't neglect CounterClockwiseContourIntegral

* Fix ~10% of cases not matching

strncmp returns 0 if the first 'len' bytes of cmark_entities[i].entity
match s; we check equal length in the first if by checking if
cmark_entities[i].entity[len] == 0, but we neglect the case where cmp ==
0 && cmark_entities[i].entity[len] != 0.  This should be treated as the
same as cmp < 0, because strcmp("abc", "abcd") < 0.

* Don't depend on py3.3 in tests

Also tools/make_entities_h.py -> tools/make_entitis_inc.py.

We dispense with the hashes and just do string comparsions.
Since the array is in order, we can search intelligently
and should never need to do more than 8 or so comparisons.

This reduces binary size even further, at a small cost
in performance.  (This shouldn't matter too much, as
it's only detectable in really entity-heavy sources.)

At least with valid data.

We now use -1 instead of 0 to indicate leaf nodes.

The primary advantage is a big reduction in the size of
the compiled library and executable (> 100K).

There should be no measurable performance difference in
normal documents.  I detected a slight performance
hit (around 5%) in a file containing 1,000,000 entities.

* Removed `src/html_unescape.gperf` and `src/html_unescape.h`.
* Added `src/entities.h` (generated by `tools/make_entities_h.py`).
* Added binary tree lookup functions to `houdini_html_u.c`, and
  use the data in `src/entities.h`.