Create dedicated documentation page for explanation math model of Bucket4j

[vladimir-bukhtoyarov]

The token bucket algorithm is well explained in many papers and wiki pages. But, Bucket4j is token-bucket on steroids, Bucket4j contain several addons to original math foundation of token bucket, but requests like this #86 point that these addons are not well explained. To close documentation dept it is need to dedicated page with many real examples which will explain all corner(and regular) cases.

[sachinkumaranumula]

+1

I am particularly interested in the GridBucket implementation rather than LocalBucket since there are few comments about Math Overflow and as to when that would occur.