Release v0.4.7

What's Changed

• docs: fix typos in TaskMetrics (by @jkosh44 in #103)
• rt: integrate derived metrics with metrics.rs (by jkosh44 in #104)
• fix: indentation in task.rs (by @arielb1 in #105)
• docs: update readme and crate documentation (by @jkosh44 in #107)
• rt: make live_tasks_count (num_alive_tasks()) stable(by @MingweiSamuel in #108)
• docs: move live_tasks_count to stable metrics in README (by @jlizen in #109)