Updates

**General Changes**
* Reduced Code complexity.
* Tidy up of code.
* Added options to the plugin to change the text and add additional classes to the generated upload field and button.
* Extracted the required CSS so people know what they can an cant strip out.
* Added a minified version to the source.
* Named the minified file to follow the defact naming convention for jquery plugin files - all lowercase jquery.

**Bug Fixes**
* Clicking cancel on upload file selector can result in the clearing of the upload input, this however doesn't reset the custom input (placeholder and button text). Input now reverts back to initial state in this instance,
* On long pages the hidden input field was not positioned correctly. Change to the positioning logic resolved this.