* Feature complete for #266 with exception of several small deviations:
1. initial image and model weight hashes use full sha256 hash rather than first 8 digits
2. Initialization parameters for post-processing steps not provided
3. Uses top-level "images" tags for both a single image and a grid of images. This change was suggested in a comment.
* Added scripts/sd_metadata.py to retrieve and print metadata from PNG files
* New ldm.dream.args.Args class is a namespace like object which holds all defaults and can be modified during exection to hold current settings.
* Modified dream.py and server.py to accommodate Args class.
