eolian: add runtime API to get file format version

This is useful for FFI based bindings (like the Lua or Python ones)
and so on.

src/bindings/luajit/eolian.lua

@@ -290,6 +290,7 @@ ffi.cdef [[
 
     int eolian_init(void);
     int eolian_shutdown(void);
+    unsigned short eolian_file_format_version_get(void);
     Eolian_State *eolian_state_new(void);
     void eolian_state_free(Eolian_State *state);
     Eolian_Panic_Cb eolian_state_panic_cb_set(Eolian_State *state, Eolian_Panic_Cb cb);
@@ -491,6 +492,7 @@ local init = function()
     eolian = util.lib_load("eolian")
     eina = util.lib_load("eina")
     eolian.eolian_init()
+    M.file_format_version = eolian.eolian_file_format_version_get()
 end
 
 local shutdown = function()

src/lib/eolian/Eolian.h

@@ -485,6 +485,15 @@ EAPI int eolian_init(void);
  */
 EAPI int eolian_shutdown(void);
 
+/*
+ * @brief Get the Eolian file format version.
+ *
+ * This is the same as the #EOLIAN_FILE_FORMAT_VERSION macro, but allows
+ * retrieval of the version at runtime, so it can be used by FFI based
+ * bindings in dynamic languages to do runtime checks and so on.
+ */
+EAPI unsigned short eolian_file_format_version_get(void);
+
 /*
  * @brief Create a new Eolian state.
  *

src/lib/eolian/eolian.c

@@ -68,3 +68,7 @@ EAPI int eolian_shutdown(void)
    return _eolian_init_counter;
 }
 
+EAPI unsigned short eolian_file_format_version_get(void)
+{
+   return EOLIAN_FILE_FORMAT_VERSION;
+}