tree bug fixed, random tree height

Please see the comments in blocks.py concerning the textures used.
names assigned to blocks, from boksee.
Fixed inventory GUI.
Merge commit '2320471b13b895db495e08315be2249bedf0ed83'

Conflicts:
	TODO.md
	blocks.py
	gui.py
	inventory.py
	main.py
Merge branch 'master' of git://github.com/avelanarius/Minecraft
Restored "hold to dig" functionality (like in MC)
Merge commit 'a552bce2c8549cd5dab18f9a9a5fe0849a450c80'
Fix default option of -terrain
Restored option to scroll in inventory.
Fix README.md
Corrected mouse clicking in inventory. You can now select items in inventory by clicking on them. After second click you can move them to quick slots.
Added new options to hide inventory GUI - by using Escape key and by clicking outside of inventory.
fix: default terrain set to 'plains' instead of 'grass'
Limit terrain argument to terrain_options.keys()
Default configuration use "plains" terrain
Bugfix
Add items names in quickslots (only selected item).
Default items should not depend on terrain flatness.
Merge branch 'master' of git://github.com/avelanarius/Minecraft
Restore the first implementation by Jimx-, which was actually correct