vsock: Prepare version 0.2.0 release

[dorindabassey]

Summary of the PR

Update changelog and Cargo.toml to version 0.2.0

Requirements

Before submitting your PR, please make sure you addressed the following requirements:

• [x] All commits in this PR have Signed-Off-By trailers (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [x] Any newly added unsafe code is properly documented.

[stefano-garzarella]

    Uploading vhost-device-vsock v0.2.0 (/home/stefano/repos/vhost-device/vhost-device-vsock)
    Uploaded vhost-device-vsock v0.2.0 to registry `crates-io`
note: waiting for `vhost-device-vsock v0.2.0` to be available at registry `crates-io`.
You may press ctrl-c to skip waiting; the crate should be available shortly.
   Published vhost-device-vsock v0.2.0 at registry `crates-io`