Update license date on all files. No functional changes.
Include __BEGIN_DECLS and __END_DECLS (i.e., extern "C" blocks) to play
well with C++.
Update licenses to 2017.
First pass at making interface for sd_notify (systemd notifications)
available (libep support only; no references). Still don't have a good
auto-compile flag; must use -DEP_OSCF_HAS_SD_NOTIFY=1 when compiling.