(modified the models so that they can use the existing shingle images instead)

(6dfacedir prediction)

instead of hundreds of nodeboxes per.

shingle

Add glass shingles : https://cdn.mediacru.sh/DJDalHp5xuNp.jpg
Textures : http://mamadou3.free.fr/shingles_glass_textures.zip

package the two together as a modpack so that regular homedecor users don't
see a functional change, but others can take signs_lib and use it as a
standalone mod.

also get rid of some *~ files

Just a minimal code reduction, but big reduction in code
duplication. This could help if in the future, support for
different "internationalization" mods will be added, or in
case Minetest supports I18N/L10N internally in the engine.

(underscore -> period).  Similarly for intllib calls and the DEBUG variable.

shingles API)

Fixed a little bug within the recipe registration which causes to
duplicate shingles when crafted from slopes.

Also changed all single quotes ' to double quotes " in crafts.lua