Handling case when diff between min and max count is smaller than size

Weights were not calculated correctly when difference between `max_count` and `min_count` was smaller than `settings.TAG_CLOUD_SIZES`. Changed calculation of weights to use floating point arithmetic. The results of weight calculations using old and new code are shown below:

http://ideone.com/fXs5aG
Merge.
Added Ahmet Bakan to AUTHORS.