I explain how to install:
This is almost as simple as compiling with the user commands "./configure", "make", and su to root to do a "make install" : the last command always installs to /usr/local/* instead of /usr, unless you add this option to the ./configure command : -prefix /usr
Here these steps have been done, all I did is pack a filesystem tree to mimick what is in the system. Here is what the package looks like:
/usr
/usr/local
/usr/local/{bin  etc games  include  lib  man  sbin  share  src}
under /usr/local/bin you have obsession-exit  obsession-logout  xdg-autostart (the binaries) and in 
/usr/local/share/locale you have the mo compiled files for the languages:
af  ast  bn     cs  el     es_VE  fa  fr   he  id  ko  ml  nl  pl  pt_BR  si  sr        te  tt_RU  ur_PK  zh_TW
am  be   bn_IN  da  en_GB  et     fi  frp  hr  it  lg  ms  nn  ps  ro     sk  sr@latin  th  uk     vi
ar  bg   ca     de  es     eu     fo  gl   hu  ja  lt  nb  pa  pt  ru     sl  sv        tr  ur     zh_CN
So to sum up, how to install ? 
Copy the whole content of the usr/local directory of this tar.xz archive to the /usr/local directory in your system, and you're done (if you do all the steps in a root console, you will not have to worry about ownership and permissions, I made sure of that when I prepared the archive : so as root "tar xfvJ OBUbuntu-obsession.tar.xz" then cd to the usr/local directory created and "cp -R * /usr/local" should do it). 
Then add obsession-logout as the command to shutdown, reboot, sleep, and so on... and you are good to go. (the two other binaries may be used or not, one future day, up to you).
One future day when I will have done a package for it, you will know where it is located and can remove it easily with a "rm -R" as root on the directories in /usr/local.