Included tick pattern options and customise grid example

I've added options to get a dashed or a dotted patter in the ticks instead of a solid line. You can set the style to "dotted", "dashed" or "solid", and an array with the dashed pattern interval. The pattern is ignored if the style is different than dashed and if nothing is given the default solid line is displayed.

The inspiration (and most of the source) came from this question on stackoverflow: http://stackoverflow.com/questions/14700417/dashed-ticklines-gridlines-in-flot

        grid: {               	        
		tickPattern: {
		         xaxis: { 
                                   style: 'dotted'  //set the tick pattern to dotted (same as dashed, [1,1])
                            },
		          yaxis: {
                            style: 'dashed', //set the tick pattern to dashed
                            pattern: [12, 2] //set the interval to 12px filled 2px empty
                        }
		 }
        }