Added Unfold Transformer
refactored command system
added 'coordOf' lens
changed more functions to lenses
Use foldMapDefault instead of mconcat + comprehension

Instead of using mconcat + comprehension, we can use foldMapDefault from
Data.Traversable, which does exactly this.

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The commit must have been lost while I rebased. Sorry for that.
Changed commands with exactly one step to LevelTrans

This allows better composability.
added mining transformation
implemented mining command
Move neighbors function from Path/Internal to Coords
Use neighbors function in Command
Apply some hlint suggestions
Merge pull request #14 from svenkeidel/commands

Commands