add --local-blob-cache-dir option to keep cached copy of blobs
[#68331718]

Signed-off-by: Gavin Morgan <gavin@pivotallabs.com>
bump version

Signed-off-by: Gavin Morgan <gavin@pivotallabs.com>
lock down to rspec 2 to fix build

Signed-off-by: Gavin Morgan <gavin@pivotallabs.com>
Improve README instructions

When installing from source, you'll likely want to bundle install unless
you JUST SO HAPPEN to have ALL THE GEMS at a correct version that the 
Gemfile specifies.

You know. Gems.
Merge branch 'master' into london