@cfg {String[]} fields
The fields of model to bind to this axis.

For example if you have a data set of lap times per car, each having the fields:
`'carName'`, `'avgSpeed'`, `'maxSpeed'`. Then you might want to show the data on chart
with `['carName']` on Name axis and `['avgSpeed', 'maxSpeed']` on Speed axis.
 
Creates new Axis.
@param {Object} config (optional) Config options.
function(config) {
        config = config || {};

        var me = this,
            pos = config.position || 'left';

        pos = pos.charAt(0).toUpperCase() + pos.substring(1);
        //axisLabel(Top|Bottom|Right|Left)Style
        config.label = Ext.apply(config['axisLabel' + pos + 'Style'] || {}, config.label || {});
        config.axisTitleStyle = Ext.apply(config['axisTitle' + pos + 'Style'] || {}, config.labelTitle || {});
        Ext.apply(me, config);
        me.fields = Ext.Array.from(me.fields);
        this.callParent();
        me.labels = [];
        me.getId();
        me.labelGroup = me.chart.surface.getGroup(me.axisId + "-labels");
    }