code: function buildAxis(){
              xAxis = d3Axis.axisBottom(xScale);
  
              yAxis = d3Axis.axisLeft(yScale)
                  .ticks(yTicks)
                  .tickPadding(yTickPadding)
                  .tickFormat(yAxisTickFormat);
          }
docs: Creates the d3 x and y axis, setting orientations
  @private