Terrawrap

Changed

- Fix bug when parsing S3 URLs while downloading plugins

Added

- Added support for downloading plugins from platform specific URLs.
For example on Mac, Terrawrap will try downloading from `<plugin_url>/Darwin/x86_64` first and fallback to
downloading from `<plugin url>`. See README for more details.

- Added support for downloading from plugins from S3 using the AWS SDK

Changed

- Changed `backend_check` to ignore directories that don't contain `.tf` files

Added

- Added support for a new `plugins` config option in `.tf_wrapper` to automatically download third party
plugins when running `init`. See the README for info.