Update Rust dependencies

[tjkirch]

Note: this is based on top of #1018; I'll fix the base branch when that's merged.

Nothing scared me; a couple compatibility updates in our code, and a bump of webpki-roots-shim to match the updated webpki-roots.

Not updated: hex-literal, because the update only seems to raise the Rust requirement to 1.45, which isn't quite in our SDK yet. (bottlerocket-os/bottlerocket-sdk#30)

Description of changes:

commit ca092dc156d65e337a3b5a7ce49ce438a6089b25
Author: Tom Kirchner <[email protected]>
Date:   Sun Aug 9 19:19:48 2020 -0700

    Add license clarification for bstr

commit ec162dec418eecb275dd78f070cf0d5b59db42de
Author: Tom Kirchner <[email protected]>
Date:   Sun Aug 9 17:15:42 2020 -0700

    Update cargo-deny config to remove no-longer-used allowances

commit 8d7fb6281edfdf46d27993ceed6f0cac4adb4151
Author: Tom Kirchner <[email protected]>
Date:   Sun Aug 9 17:05:59 2020 -0700

    Update Rust deps in tools/
    
    There were only minor compatibility changes required in buildsys (from sha2).

commit 2ae389a733246b45be33af033dc110e135b9ce94
Author: Tom Kirchner <[email protected]>
Date:   Sun Aug 9 17:04:39 2020 -0700

    Update Rust deps in sources/
    
    There were only minor compatibility changes required in schnauzer (from
    handlebars) and updog (from tough).

Testing done:

aws-k8s-1.15, 1.16, and 1.17 all run multiple pods OK, services start OK, and updog is able to pull and apply an update. aws-ecs-1 ran a task OK.

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.