Improve the output of `hit fetch`

Previously:

    $ hit fetch http://llvm.org/releases/3.4/libcxx-3.4.src.tar.gz
    Downloading http://llvm.org/releases/3.4/libcxx-3.4.src.tar.gz...
    Downloading 'http://llvm.org/releases/3.4/libcxx-3.4.src.tar.gz'
    [=========================] 100.0% (1.3MB of 1.3MB) 2.418MB/s ETA 0s

    tar.gz:xwpsaatz6dvrt7bi5uwz2yd57u4ofz6z

Now:

    $ hit fetch http://llvm.org/releases/3.4/libcxx-3.4.src.tar.gz
    Downloading http://llvm.org/releases/3.4/libcxx-3.4.src.tar.gz...
    Downloading 'http://llvm.org/releases/3.4/libcxx-3.4.src.tar.gz'
    [=========================] 100.0% (1.3MB of 1.3MB) 3.022MB/s ETA 0s

    url: http://llvm.org/releases/3.4/libcxx-3.4.src.tar.gz
    key: tar.gz:xwpsaatz6dvrt7bi5uwz2yd57u4ofz6z

The output can now be copy & pasted into the package.yaml