Fixes copyright header.
Begins implementation of mcmapgen. A new command line tool, which
generates a google-maps like map interface for a single, given
Minecraft world.

This will eventually replace the mcra webserver as a standalone
HTML5 application. Along with display of a 2D map of the world, it
allows display of various informative overlays and analysing of
block regions for their contents.
Completely rewrites anvil/nbt package.
It now exposes a single Unmarshal() function, which works in
a similar way to Go's json.Unmarshal. You define a struct with
appropriate field tags to decode nbt data into.
For example:

	type LevelData struct {
		Player     PlayerData `nbt: "Player"`
		Rules      GameRules  `nbt:"GameRules"`
		LastPlayed time.Time  `nbt:"LastPlayed"`
		Name       string     `nbt:"levelName"`
		Seed       int64      `nbt:"RandomSeed"`
		DayTime    int64      `nbt:"DayTime"`
		GameType   int32      `nbt:"GameType"`
		Thundering bool       `nbt:"thundering"`
	}

	type Level struct {
		LevelData `nbt:"Data"`
	}

It supports a small set of implicit type conversions, in order
to make using the data easier.

    Tag Id         | Assignable to field      | Note

============================================================================
    TAG_Byte       | int8, uint8              |
                   | bool                     | true if the tag value is
1.

----------------------------------------------------------------------------
    TAG_Short      | int16, uint16            |

----------------------------------------------------------------------------
    TAG_Int        | int32, uint32            |

----------------------------------------------------------------------------
    TAG_Long       | int64, uint64            |
                   | time.Time                | Expects a Unix
timestamp.

----------------------------------------------------------------------------
    TAG_Float      | float32                  |

----------------------------------------------------------------------------
    TAG_Double     | float64                  |

----------------------------------------------------------------------------
    TAG_Byte_Array | []int8, []uint8          |

----------------------------------------------------------------------------
    TAG_Int_Array  | []int32, []uint32        |

----------------------------------------------------------------------------
    TAG_String     | string                   |
                   | bool                     | true if tag value is
                   | time.Time                | Requires an additional
struct
                   |                          | field tag to hold the
time
                   |                          | format:
`time:"2006-01-02"`

----------------------------------------------------------------------------
    TAG_List       | []T                      |

----------------------------------------------------------------------------
    Tag_Compound   | struct T                 |

----------------------------------------------------------------------------

Any other, incompatible assignment will result in a parse error.
Deletes some unnecessary files.
Fixes bug in unmarshaling of byte literal.
Fixes nbt package documentation.
Fixes the anvil package to reflect the rewriting of anvil/nbt.
Fixes test code and applies further work to mcmapgen tool.