Update tooltip.js

Fix whitespace in README.md

Merge branch '1033_custom_legend_config' of https://github.com/davidpoore/c3 into davidpoore-1033_custom_legend_config

Calling resize on each and every window resize drammatically slows down the browser

Add a Gitter chat badge to README.md

Add title config option to c3 charts core

 When any graph is opened in iOS devices, clicking on a point highlights the whole graph with gray color briefly. This hinders the interactivity as it does it for the whole graph area