add support for array of tick label strings #139

formatted tick label can be an array of strings, each will be displayed
in a line

c3.js

@@ -6456,7 +6456,7 @@
                 text = tick.select("text");
                 tspan = text.selectAll('tspan')
                     .data(function (d, i) {
-                        var splitted = params.tickWidth ? splitTickText(d) : [textFormatted(d)];
+                        var splitted = params.tickWidth ? splitTickText(d) : [].concat(textFormatted(d));
                         counts[i] = splitted.length;
                         return splitted.map(function (s) {
                             return { index: i, splitted: s };

src/c3.axis.js

@@ -149,7 +149,7 @@ function c3_axis(d3, params) {
             text = tick.select("text");
             tspan = text.selectAll('tspan')
                 .data(function (d, i) {
-                    var splitted = params.tickWidth ? splitTickText(d) : [textFormatted(d)];
+                    var splitted = params.tickWidth ? splitTickText(d) : [].concat(textFormatted(d));
                     counts[i] = splitted.length;
                     return splitted.map(function (s) {
                         return { index: i, splitted: s };