Add stars count

We are you using rating to our products, from 1 to 5 stars, so using gorse, I can add one star for the item.

We have 2 suggested solutions:

1. Add value for the stars to get the exact value to run through gorse. the value can be a float between 0 and 1.
2. Add a negative feedback opposite of the star, so if user vote with 3 stars, we can ignore, if 4 or 5 we can send a star, if 1 or 2 we can send a negative star. which will be easier in development. and can help when someone uses like and dislike buttons.

Review how Gorse currently represents item ratings and positive or negative feedback. Resolve whether the change should preserve an exact star value or map ratings to positive and negative feedback, then define the API behavior and tests that demonstrate the chosen approach is complete.

Written by the indexing model from the issue text.