Release 0.3.0

Once again, this release was cut to ensure generated code passes lints.

Breaking changes

• Changed TreeMatcher::new() to accept std::fmt::Display instead of AsRef<str>, since we convert to a String with to_string() regardless. This is very unlikely to break anything.
• Changed TreeNode::render_iter() to accept std::fmt::Display instead of AsRef<str>, since we use the parameters in format strings. This is very unlikely to break anything.

Changes

• Switched code to disable Clippy to use cfg(clippy) instead of cfg(feature = "cargo-clippy"). The feature has been deprecated.