prepare v0.2.12 release (tokio-rs#93)

prepare v0.2.11 release (tokio-rs#87)

Release v0.2.10 (tokio-rs#81)

prepare v0.2.9 release (tokio-rs#75)

Prepare v0.2.8 release (tokio-rs#71)

prepare v0.2.7 release (tokio-rs#67)

prepare v0.2.6 release (tokio-rs#64)

prepare v0.2.5 release (tokio-rs#49)

prepare v0.2.4 (tokio-rs#45)

Prepare v0.2.3 release (tokio-rs#43)