Added msgfmt_args arg to i18n.gettext

i18n.gettext now supports the msgfmt_args argument. This argument can be used to pass additional arguments to msgfmt when building the translations.

i18n = import('i18n')
i18n.gettext('mycatalog',
             args : ['-k_', '-kN_'],
             msgfmt_args : ['--use-fuzzy'])