Support for triggering the resize of each textarea when the plugin is initialized

A new `onInitialize` option *(defaulting to `false`)* will call `resize()` internally when the plugin is initially called for some `selector`.

This allows a textarea with a default value that 'taller' than the height of the textarea to be resized without requiring an input from the user.
Merge pull request #5 from deefour/patch-1

Support for triggering the resize of textarea when the plugin is inialized