V3

Add:

• skyboard_collide.lua (node collider lib)
• skyboard_minetest_ext.lua (extend minetest API)
• upgrade node collider for entity

groundboard

• collide up + test case up
• collide down + test case down
• small auto jump
• climb on wall

skyboard

• small auto jump
• unlimited flight
• fall when collide

Delete:

• move entity left,right (collider bug source)