Fix keydown error

* I fixed the error which referenced the data of undefined `$cellB` in
  `Plugin.prototype.keydown` by making it return when the input key
  code is not an arrow key or shift key.
Modify the extra parameter of `selectionupdate`

* Now the extra parameter is passed as an plain object, not an array,
  because there are more than one data which are passed.
* The object array of selected cells can be accessed with
  `selectedCells` key from the extra parameter object.
* The list of new data passed as the parameter is below.

    * The number pair array of selected cells. Each object in the
      array is in a form like `{ row: 1, col: 2}`. This can be
      accessed with `selectedCellsNo` key.
    * The last selected cell object. This can be accessed with
      `lastSelectedCell` key.
    * The mouse position of `mouseup` event at the last selected cell
      (only when the selection was ended with `mouseup` event). This
      can be accessed with `pageX` and `pageY` key, which means
      the x-value and y-value of the position.

* The example code has been updated.
Fix more-than-one-digit bug

* As the string was not converted into number in
  `Plugin.prototype.updateSelectedCells` function, when the most
  significant digit of larger index was smaller than that of smaller
  index, selected cells were not calculated correctly.

* I replaced `parseInt` function usage with unary `+` operator, which
  also converts string into number.
Add `update` command

* Updating procedure of cells in the table is now separate from
  `Plugin.prototype.init` method into `Plugin.prototype.update`.
* The `update` command can be given by calling the plugin function
  like `$('#selectable').selecTable('update')`.
* When the number of rows and cells of a `<table>` element was
  changed, the `update` command should be given to make the plugin
  work correctly.
* The example code was updated.
Add UglifyJS script

* Minified and uglified version of script can be generated by
  executing `uglify.sh`.
* Minified and uglified version of script was updated.