Allow queries to be specified as a dict.

Adds the ability for the queries parameters to be defined as a mapping
of zoom level to the query.  Undefined zoom levels are assumed to be null.
Allow S3 policy to be specified in config

Adds an optional 'policy' field to the S3 configuration allowing specific
permissions to be specified. The default is 'public-read'.
Return a transparent tile if coord is out of bounds.
Add 'scale factor' option to Mapnik image provider

Adds the optional 'scale factor' argument in the config for Mapnik's
image provider. Allows a TileStache layer to be configured for retina.
Properly document 'scale factor' option.

Remove improper underscore
correct documentation for layer_id_key, layer_index
Add responding to "/favicon.ico"
Remove unnecessary dict update.
Merge pull request #157 from jwass/scale_factor

Add 'scale factor' option to Mapnik image provider
fix Pillow dependency
Merge pull request #196 from slafs/PILfix

fix Pillow dependency
Merge pull request #195 from garnertb/minutia

Remove unnecessary dict update.
Merge pull request #194 from ypyf/master

Add responding to "/favicon.ico"
Revert "Add responding to "/favicon.ico""
Merge pull request #197 from TileStache/revert-194-master

Revert "Add responding to "/favicon.ico""
enable "cache lifespan" in Redis cache
Updated Vagrantfile link (refs #200)
Merge pull request #201 from juliomalegria/master

Updated Vagrantfile link (refs #200)
Merge pull request #198 from wilsaj/enable-redis-cache-lifespan

enable "cache lifespan" in Redis cache
Merge pull request #192 from talin-trulia/master

correct documentation for layer_id_key, layer_index