Adds access & destination config options for grunt-aws

[moladukes]

1. While setting up s3 I was getting Access Denied errors which were solved by passing an Access permission option.

access (String)
Default "public-read"

File permissions, must be one of:

"private"
"public-read"
"public-read-write"
"authenticated-read"
"bucket-owner-read"
"bucket-owner-full-control"

2. Once passing the correct access permission (in my case private) the upload worked! However a new problem arose; They were getting dumped into root.

grunt-aws has a dest (String) option which allows you to specify where to upload the files. By including this option my use case/set up was complete.

      build: {
        cwd: path.images_src,
        src: '**',
        dest: "<%= config.s3.dest %>"
      }

3. Another potential "Fix" would simply add these edge cases to the Wiki however I think them common enough for them to be in the example/default configs.