Patch for #1141

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

Sudhakar, Hemanth | Added a config called 'sensitivity' for the point so that click sensitivity can be configured.

Right now, the click area of a point is hard coded in the code and in high pixel density devices (iPad) this is not enough. Have modified the data.js (c3_chart_internal_fn.dist) function to calculate the distance between the two points and compare it with the configured value (which is passed to c3.generate method along with other config)

 Example

         point: {
             show: true,
             r: 5,
             sensitivity: 20
         },