Add LIBFREEM_API_VERSION macro and make repeated freem_init calls idempotent

1 job for nodem-fixes in 24 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
failed #769
freem

00:00:24

 
Name Stage Failure
failed
freem Build
     mlib_initialized
mlib.c:120:5: note: each undeclared identifier is reported only once for each function it appears in
make[2]: *** [Makefile:2232: freem-mlib.o] Error 1
make[2]: Leaving directory '/home/gitlab-runner/builds/xNFezvFm/0/jpw/freem/src'
make[1]: *** [Makefile:626: all] Error 2
make[1]: Leaving directory '/home/gitlab-runner/builds/xNFezvFm/0/jpw/freem/src'
make: *** [Makefile:830: all-recursive] Error 1
Cleaning up file based variables
ERROR: Job failed: exit status 1