Release of 1.5.8

- 1f6e9d4172a65b7faf06425afbb627ae603247e8: Merge pull request #1419 from mattrjacobs/never-let-maximum-size-and-core-size-diverge-unless-user-opts-in
- ef5047d64c9409e68b6b6ff20cbd1afb8ecf0191: When user has not opted in to letting core/maximum threadpools diverge, ensure dynamic updates to coreSize apply to both
- b7b955b629c2be19f628321094c2008b3974b277: Merge pull request #1415 from starlight36/master
- 49922d350b1c8c5711ef209fbcb0cf71463d88b4: Fix a little spell mistake in comments.
- 7598e9a68d81f84de9956758ee1cf0c176d9031f: Add v1.5.7 to CHANGELOG
