Convert audioc to lopsub.

This changes para_audioc to use the lopsub library rather than
gengetopt for parsing the command line options. The gengetopt input
file m4/gengetopt/audioc.m4 is replaced by an equivalent suite file,
audioc.c is adjusted to call the lopsub primitives instead if the
gengetopt parsers, and para_audioc is linked against lopsub. Moreover,
the manual page of audioc is now generated with lopsubgen.

Since this is the first executable which is converted, the commit
introduces a fair amount of infrastructure which will also be used
by other executables. Specifically:

* Common command line options (--help, --detailed-help, --version,
--loglevel, --history_file, --complete) are stored in per-option
files below m4/lls/include. Each of these files is included from
audioc.suite.m4. To tell make which files audioc.suite depends on,
we use the line synchronization feature of m4 and a simple awk script
to create a .m4d file which contains these dependencies, similar to
the .d files which describe dependencies of .c and .h files. The new
m4_lls_deps make variable contains the set of .m4d files.

* A generic copyright section for the man page which refers to the
COPYRIGHT_YEAR macro, defined from the make variable in Makefile.real.

* The new make variable LOGLEVELS. We need to know the set of loglevels
in the suite files as well as in the C code, so the variable avoids
to duplicate this information.