If you want to build tvheadend from source, please visit this page. Please notice that wiki development site only reflects the work in HEAD (-current). It should not deviate much should you want to build a released version from source, but you never know.
Tvheadend is part of the HTS project hosted at http://hts.lonelycoder.com/.
It functions primarily as a TV backend for the Showtime Mediaplayer but can be used standalone for other purposes.