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
Rename parameter for consistency.

The declaration for parse_overrides() mismatched the definition,
causing doxygen warnings.
Doxyfile generated from version 1.8.6.
Add version info to Doxyfile.

Rename to Doxyfile.in and add to AC_CONFIG_FILES for proper
PACKAGE_VERSION substitution.
Ignore generated Doxyfile in git.
Merge branch 'release-0.1' into develop

Conflicts:
	configure.ac