Update texture asset locations
added XYZRange namedtuple to isometricrenderer for increased readability

Replaces chunkbox[0][1] and sectionbox[1][0] and such with chunkbox.miny
and sectionbox.maxx, etc
minor changes to chunkrenderer and dispatcher

adjusted a comment in chunkrenderer

changed dispatcher to use a default dummy observer if none was provided.
Added IsometricSingleBlockRenderer renderer class

Also split some common functionailty between the two isometric renderers
into a base class.
Updated texture finding, based on master branch
Merge remote-tracking branch 'michael/oil' into oil
added hack texture path option to command line.

This kind of throws away the value from the config file but config files
are broken right now anyways
added blockviewer.py script

Generates a sequence of frames each rendering the given block. Uses
imagemagick to coalesce them into a GIF. Uses the new
IsometricSingleBlockRenderer and the SingleImageCanvas.