Clear up createIndex docs

[msmuenchen]

For those who are not used to either native IndexedDB or jquery-indexeddb, the behavior of jquery-indexeddb's createIndex compared to native is totally reversed.

The spec says for createIndex (https://developer.mozilla.org/en-US/docs/Web/API/IDBObjectStore#createIndex()): in name, in keyPath, but jquery-indexeddb uses in keypath, in name without explicitly saying that this is the exact opposite of the API specs!