Bump eventree to 0.7.0

[lunacookies]

eventree 0.7.0:

• the SyntaxKind trait has been eliminated in favor of a few more methods on TreeConfig
• &SyntaxTree is now a direct pointer to the syntax tree’s data, rather than a pointer to a pointer. In order to accomplish this, SyntaxTree is now an unsized type and a new type SyntaxTreeBuf is introduced to own the allocation. &SyntaxTree and SyntaxTreeBuf have the same relationship as e.g. &str and String or &Path and PathBuf.
• the tree no longer stores finish node events explicitly, which sometimes gives a small perf boost