Extract contributor changelog description from PR body
Extract contributor changelog description from PR body

Now, if PR description contains `changelog: %some description%`, it will be used as description of the corresponding item in changelog template

intellij-rust/intellij-rust.github.io,intellij-rust/intellij-rust.github.io,intellij-rust/intellij-rust.github.io,intellij-rust/intellij-rust.github.io