Update packages and documentation

• Updates packages following Greekeeper recommandations : #8
• Update doc with badge

Refactoring following sonarcloud.io recommandations

v2.2.0

Refactoring following sonarcloud.io recommandations

New feature: instance has now a property "meta"

It that contains global stats about the data (words number, characters, etc).
Read the documentation: https://github.com/proustibat/occurences/blob/master/README.MD#properties

Improve getSorted method

Fix the issue about possible wrong result in getSorted method. Please read #4

Breaking change: getSorted() now returns an array. Read the documentation here : https://github.com/proustibat/occurences/blob/master/README.MD#methods