Make stone pebbles more useful

[Wuzzy2]

Suggestion:

• Make (red) stone pebbles diggable by hand
• Make pickaxe dig time for pebbles much shorter
• Add craft: 9 (red) stone pebbles give 1 (red) cobblestone.
• Add stone pebbles to other biomes in the world

This will give the player an interesting new way to craft tools, different from the odd “tree punching”. :D

What do you think about this?

[vlapsley]

Commit https://github.com/vlapsley/outback/commit/4bb1cb5f75f6bd6f64a5dec0d2286f3f5843b014 introduces small rocks, replacing the pebble.

Modified code from duane-r valleys_c I like the look of the little cubes vs. the pebbles sphere. Fits with the game better, IMO.

3 types: red stone, sandstone and default stone. 4 small rocks is craftable into cobble.

I've made a sandstone cobble node. I'm not sure about the texture though.

I'll nerf tree-punching in a future commit.