escape & and  = in query values

needed for response-content-disposition
#url_for supports :query for custom query params

AWS::S3::S3Object#url(:query => {})
AWS::S3::S3Object.url_for(name, bucket, :query => {})
AWS::S3::S3Object.path!(bucket, name, :query => {})
escape ; in query values too
Merge pull request #2 from github/url_for-with-parameters

Url for with parameters