Allow setting of fileupload options through s3uploader

[ryanwood]

This is a fairly simple change to address #125. I created a new settings option called fileupload_options which defaults to null. By passing any valid option from https://github.com/blueimp/jQuery-File-Upload/wiki/Options you can set the option directly in the fileupload plugin.

I simply moved all of the fileupload function overrides to an api object and them extended them with the new settings option. I intentionally made it so that someone could override even the s3uploader default API in case they wanted to extend it.

Let me know if you have any questions.

[sheerun]

It is possible in my spin-off gem: https://github.com/sheerun/s3_file_field

[andrewjdmccann]

If anyone runs into this issue and comes across this pull request there's a (somewhat fragile) work around until this PR or similar gets merged. It relies on the fact that s3_direct_upload leverages jQuery-File-Upload but that's unlikely to change, so this should be pretty safe.

jQuery-File-Upload allows you to set some of it's options via data attributes.
https://github.com/blueimp/jQuery-File-Upload/wiki/API#data-attributes

s3_uploader_form(
  # ...
  :data => {
    # ...
    :drop_zone => ".my-dropZone-selector"
  }
)