add dynamic version to build via meson

remove unused arg in misc
mark arg as unused in addtax
update translations

src/include/addtax.h.in

@@ -0,0 +1,3 @@
+#define _(STRING) gettext(STRING)
+#define TAX 1.111111111
+#define VERSION "@version@"

src/include/meson.build

@@ -0,0 +1,5 @@
+conf_data = configuration_data()
+conf_data.set('version', meson.project_version())
+configure_file(input : 'addtax.h.in',
+	output : 'addtax.h',
+	configuration : conf_data)

src/include/misc.h

@@ -0,0 +1 @@
+bool is_float(const char *string);