Fixed project URL.
Enhanced 'find-prefix' to work with bare digests.

This lets you use commands like 'blob info 2a4' to pick out a blob
without needing to type out the 'sha256:' prefix every time. The
algorithm defaults to whatever the blob-store uses.
Add more metadata to blob info from file store.

This includes `:location` with a file:// URL and `:content-type` with a MIME
guess provided by the `file` command.
Fix bug related to CLJ-124.
Add --pretty option for 'blob info' command.
Refactor blob-store initialization in tool.clj.