Ensure variables are declared at the top of the block.

New version has axis flags.

New API:
+hb_ot_var_axis_info_t
+hb_ot_var_find_axis_info()
+hb_ot_var_get_axis_infos()

Deprecated API:
-HB_OT_VAR_NO_AXIS_INDEX
-hb_ot_var_axis_t
-hb_ot_var_find_axis()
-hb_ot_var_get_axes()

Should increase coverage...