fix to match README syntax

[athibaud]

• the asset README indicates that you can specify a ./assets.json like so:
  { "jquery": "1.7.2", "backbone": "0.9.2" }
  but in the code you were expecting this syntax:
  { "jquery": { "version": "1.7.2" }, "backbone": { "version": "0.9.2" } }
  fixed to match README syntax.
• when compress is defined in the ./.asset file, the options isn't accounted for when asset uses the ./assets.json file. fixed.

[athibaud]

would you mind accepting this?
I still use asset (my fork of it for now) but npm doesn't like git dependencies too well.

[athibaud]

thank you, just needs that final push to the npm : )