README : Update sha256 hash of package

Updated sha256 hash of etcd-v0.5.0-alpha.4-linux-amd64.aci
Merge pull request #287 from rahulgopan/master

README : Update sha256 hash of package
*: Use sha-512 digest format

Per appc/spec#8, we should be using sha-512 hashes for speed
cas: tweaks and added tests

Mostly addressed comments in https://github.com/coreos/rocket/pull/209
- errors should start with lowercase
- split out consts for hash prefixes/lengths
- added tests for ResolveKey
- added test to check for unexpected goroutines
- revert to panicking if we get unexpected input to blockTransform