https://github.com/google/gumbo-parser is an implementation of
http://www.w3.org/TR/html5/syntax.html implemented as a pure C99 library
with no outside dependencies.

Goals and features of the C library:

* Fully conformant with the HTML5 spec.
* Robust and resilient to bad input.
* Simple API that can be easily wrapped by other languages. (This is one
of such wrappers.)
* Support for source locations and pointers back to the original text.
(Not exposed by this implementation at the moment.)
* Relatively lightweight, with no outside dependencies.
* Passes all html5lib-0.95 tests.
* Tested on over 2.5 billion pages from Google's index.