Fixed - updated readme to describe `upstreamArtifacts` rather than `unsignedArtifacts`.
Removed - `valid_artifact_*` config items, as well as references to them in the readme.
0.8.1
Fixed - bumped the token timeout to 20min
0.8.0
Changed - `copy_to_artifact_dir` is now `copy_to_dir`, and takes a `parent_dir` arg.
Fixed - copy `upstreamArtifacts` files from `artifact_dir` to `work_dir` before signing. This means we no longer overwrite chain of trust artifacts with signed artifacts
0.7.1
Fixed - only copy files that aren't already in the appropriate `artifact_dir` location
0.7.0
Changed - changed the task definition to use `upstreamArtifacts`, which allows for different sets of signing formats per file - stopped downloading artifacts; now we use the pre-downloaded files from scriptworker's chain of trust verification
0.6.0
Changed - moved `download_artifacts` and `download_files` to scriptworker; compatible with `scriptworker>=0.7.0`
Fixed - noted that the various `*_dir`s need to be absolute paths.
Removed - `DownloadError`, which is now in scriptworker, and `ChecksumMismatchError`, which wasn't used.