Add dot_match option to S3 provider

When collecting files to upload, optionally include dot files
Fixes https://github.com/travis-ci/dpl/issues/148
Add dot_match option to cloud_files provider

When collecting files to upload, optionally include dot files
Add dot_match option to gcs provider

When collecting files to upload, optionally include dot files
Document `:dot_match` option for GCS, Rackspace, and S3