v.0.8

add initial support for python 3.7 and 3.8
added options StandardOutputFile, StandardOutputFileToAppend, StandardErrorFile and StandardErrorFileToAppend to known unit signatures.
Added type stubs for pystemd.daemon, pystemd.dbuslib, pystemd.systemd1.Unit and pystemd.systemd1.Manager because we still "support python 3.4.
fix issue when char is unsigned, and <char *> -1 returns 255.
added slice_ option to pystemd.run to specify the cgroup where the unit is created.