stage1: fix bad path reference :-(
cas: write download progress to stdout

Using mitchellh/ioprogress, implements a visual for the process of
downloading an aci.

Fixes #208.
Merge pull request #231 from jzelinskie/master

cas: write download progress to stdout
*: Using sha512 instead of sha256
*: Update documentation for sha512, fix missing
*: More sha512 documentation updates
appc: Dont support sha256 for hash at all
Use hash prefixes for rkt run/fetch
appc/spec: updating documentation for prefixes
gofmt
cas: use KeysPrefix diskv method