Adds a parameter to disable syncing

[da1nerd]

Some times you just want to upload files without downloading everything. This is especially helpful when when uploading larges files like builds because I don't want to download everything I've already uploaded and waste time and bandwidth.

Now when using this resource you can use a sync flag to disable the syncing. For example:

- name: upload
  type: my-s3-folder
  source:
    bucket: my-s3-bucket.com
    ...
    sync: false
    options:
      - ...

The the default action is to sync so this shouldn't break existing configurations.