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 all the data set is zero the label should be in the above of the y
axis

When all the data set is negative the label position of cero value will
be above the the y axis line then you will not see the label.