Fixes tooltip callbacks, set return and data type
Fixes tooltip callbacks, set return and data type

http://www.chartjs.org/docs/latest/configuration/tooltip.html#tooltip-callbacks

All functions are called with the same arguments: a tooltip item and
the data object passed to the chart. All functions must return either
a string or an array of strings

chrootsu/DefinitelyTyped,laurentiustamate94/DefinitelyTyped,georgemarshall/DefinitelyTyped,zuzusik/DefinitelyTyped,rolandzwaga/DefinitelyTyped,zuzusik/DefinitelyTyped,one-pieces/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,aciccarello/DefinitelyTyped,rolandzwaga/DefinitelyTyped,magny/DefinitelyTyped,arusakov/DefinitelyTyped,aciccarello/DefinitelyTyped,arusakov/DefinitelyTyped,AgentME/DefinitelyTyped,dsebastien/DefinitelyTyped,zuzusik/DefinitelyTyped,arusakov/DefinitelyTyped,chrootsu/DefinitelyTyped,AbraaoAlves/DefinitelyTyped,AbraaoAlves/DefinitelyTyped,aciccarello/DefinitelyTyped,georgemarshall/DefinitelyTyped,alexdresko/DefinitelyTyped,mcliment/DefinitelyTyped,borisyankov/DefinitelyTyped,alexdresko/DefinitelyTyped,dsebastien/DefinitelyTyped,benliddicott/DefinitelyTyped,markogresak/DefinitelyTyped,AgentME/DefinitelyTyped,georgemarshall/DefinitelyTyped,magny/DefinitelyTyped,borisyankov/DefinitelyTyped,AgentME/DefinitelyTyped,AbraaoAlves/DefinitelyTyped