I've tested this on a clean Debian Jessie install. Seems that libhdhomerun-dev provides /usr/include/libhdhomerun/hdhomerun.h, but that package isn't a dependency for tvheadend in this repository (tested with stable and release). This is a problem because tvheadend looks for this file during compile-time. As such, I think that the latest binaries for TVHeadend don't include hdhomerun support. If you rebuild for your machine with libhdhomerun-dev installed, I think it will work.
I do not actually think that this is a bug since Scott Harris reports that release 1321 does in fact work.
Try to apt-get source, and rebuild via debian/rules binary (iirc, I don't use debian-like distros anymore ;)) with libhdhomerun-dev installed.
p.s. I've been using the bintray repo!