Allow non-string arguments for minetest.is_yes()
Use the Settings Lua interface to read world.mt
Use engine.is_yes() in mainmenu
Fix bug: texture pack not overriding default menu textures
Add offset to automatic_face_movement_dir
Fix hotbar padding at bottom
Change mainmenu texture handling + small misc changes

Texture names must now be escaped in formspec elements image[],
background[], image_button[], image_button_exit[].

Instead of special-case handling of texture loading (and unloading
which was missing) in guiFormSpecMenu.cpp, use the newly created
ISimpleTextureSource interface which is a minimal subset of
ITextureSource. There is an implementation of this interface
used by GUIEngine (MenuTextureSource).

Fix an off-by-one bug in unescape_string; it caused requests for a
texture called "\0".
Add formspec table and reorganize formspec helper docs a bit

Also rename engine.get_textlist_index to engine.get_table_index