Remove obsolete FIXMEs.
Update email address for package.
Do not treat compiler warnings as error by default.

Remove the -Werror flag from the default compiler options.  It tends
to cause more trouble in released versions, so should only be used
during development.
Add proper version information to Argp parser.

Reuse PACKAGE_VERSION macro for the version string.
Call AC_USE_SYSTEM_EXTENSIONS before C compiler check.
Fix crash if no argument parser children are defined.
Remove -Werror from Makefile.simple.
Fix Makefile.simple to work with current code.