* core: add ZipPath encapsulating compressed zip files
this way you don't have to unpack it first and can work as if it's a 'virtual' directory
related: https://github.com/karlicoss/HPI/issues/20
- rely on appdirs for default cache path instead of hardcoded /var/tmp/cachew
technically backwards incompatible, but no action needed
you might want to clean /var/tmp/cachew after updating
- use default cache path (e.g. ~/.cache) by default
see https://github.com/ActiveState/appdirs#some-example-output for more info
*warning*: things will be cached by default now (used to be uncached before)
- treat cache_dir = None in the config
*warning*: kind of backwards incompatible.. but again nothing disasterous
