Consider switching http-parser to llhttp

[micwoj92]

http-parser is not actively maintained and maintainers suggest switching to llhttp https://github.com/nodejs/http-parser/issues/522

[hdholm]

I poked at this a little and got things compiling, but not yet working. Someone smarter than me could probably make this transition easily. However, while llhttp is in the FreeBSD, Fedora, and EPEL repos, it looks like the Debian family of Linuxes haven't incorporated llhttp yet.