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.
correct documentation for layer_id_key, layer_index
enable "cache lifespan" in Redis cache
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
Merge pull request #168 from byrman/byrman_fix-bounds-option

Return a transparent tile if coord is out of bounds.
Merge pull request #156 from jwass/s3_policy

Allow S3 policy to be specified in config
Merge pull request #144 from jwass/queries_dict

Allow queries to be specified as a dict.
Merge pull request #204 from juliomalegria/master

Added 'pixel effect' as a Layer parameter