Added show options to x and y axis.
Added show options to x and y axis.

mdavid5/c3-angular-directive,Eden-Sun/c3-angular-directive,panbhatt/c3-angular-directive,jettro/c3-angular-directive,hfreire/c3-angular-directive,Eden-Sun/c3-angular-directive,matheusdavidson/c3-angular-directive