Fix for issue #121

In handleKeyPress method, I've added a 'self' variable pointing to 'this':
```javascript
SelectBox.prototype.handleKeyPress = function (event) {
    var select = $(this.selectElement)
        , control = select.data('selectBox-control')
        , options = control.data('selectBox-options')
        , self    = this;
```
And below, in the default part of the switch, I've replaced some 'this' references to 'self' references, as they were out of context:
```javascript
options.find('A').each(function () {
      if ($(this).text().substr(0, self.typeSearch.length).toLowerCase() === self.typeSearch.toLowerCase()) {
          self.addHover($(this).parent());
          self.selectOption($(this).parent(), event);
          self.keepOptionInView($(this).parent());
          return false;
      }
  });
  // Clear after a brief pause
  this.typeTimer = setTimeout(function () {
      self.typeSearch = '';
  }, 1000);
```