* Refactor Azure Pipelines config and tweak releases
* Extract out doc/rustfmt jobs into their own separate builders. Helps
avoiding having to skip tons of steps and can get failing results more
quickly.
* Extract out Rust installation logic to a dedicated template.
* Separate out the build/test job matrices, where one matrix runs tests
and another runs a full build
* Refactor release directory structure to follow a convention where
`foo.tar.gz` extracts to a folder called `foo` and follow unix-like
conventions and copy over the license/readme files into the release
tarballs.
* Swap order of build/test
This Azure Pipelines setup compiles and tests Wasmtime for Linux, macOS, and Windows.
If the CI run was triggered by a new tag being created, a new release for that tag is created with a changelog relative to the last tag release and archives of the builds for all platforms.
If the CI run was triggered by new commits landing on `master`, the release `latest-master` is updated with a new changelog relative to the last tag release and archives of the new builds for all platforms.
Note: This PR also contains changes to disable a bunch of tests on Windows, which are failing due to issues with signal handling.
