Add basic GNU gettext infrastructure.
Fix non-constant string initializers in known_fields.

Use no-op gettext macro for string constant.
Remove explicit _XOPEN_SOURCE definition.

The feature test macro should be defined during configuration and
conflicts with libintl.h.
Incorporate gettext.h for i18n.
Initialize i18n in main().
Update specified gettext version to 0.18.3.
Add POTFILES.in list.
Merge branch 'gettext' into develop

Conflicts:
	Makefile.am
	configure.ac
Merge branch 'release-0.1' into develop

Conflicts:
	configure.ac
Add configuration files for GNU Gnulib.

Gnulib provides implementations for the not-so-portable functions used
in this codebase, namely the argp program options parser and the
related getsubopt() function.  gnulib-tool takes care of importing the
required modules using the gnulib-cache.m4 file.
Modify build system to include Gnulib.

Add the required configuration flags for autoconf and automake to
build gnulib modules before our own sources which depend on the
functionality.  Add gnulib-cache.m4 to EXTRA_DIST for use in source archives.
Add dummy file gnulib/.gitignore.

This avoids automake warnings when the gnulib directory is missing.
Make GNU Gnulib usage optional.

Hide the gnulib configuration macros behind m4_ifdef() conditionals.
Add USE_GNULIB conditional for automake to skip subdir if not in use.
This allows compilation of a source tarball without first invoking
gnulib-tool.
Ignore some files added by gettextize.
Check USE_GNULIB in src directory.
Merge branch 'gnulib' into develop
Bump program version to 0.2.
Add comment about Gnulib handling.
Add a minimalistic ChangeLog.
Merge branch 'release-0.2'