ZIO Core
* Added `FiberRef`, a version of `FiberLocal` that's inherited by child fibers on forks and joins (665) (618)
- Added `inheritFiberRefs`
* `ZStream` now tracks finalization scopes as part of the stream computations. This means that resources are acquired and released more precisely as part of the stream, including across concurrency combinators such as `buffer`, `zipWith` and `merge`. (906)
- `ZStream` uses `ZManaged` as the return type for stream folds
- Several concurrency combinators were added: `ZStreamflatMapPar`, `ZStream.flattenPar` and `ZStream.mergeAll`.
* Added ZIO Tracing for the JVM - `Cause` now includes a `ZTrace` with the fiber's monadic stack trace, execution trace and traces of parent fibers at time of failure. (849)
- added a new branch to `Exit.Cause` - `Cause.Traced`
- Added `trace`, `traced`, `untraced`, `refailWithTrace`, `tracingStatus` and `checkTraced`
- Added `haltWith`
- `Platform` now has a `tracing` field for tracing configuration
* `ZManaged` API has been significantly extended, most of the `ZIO` methods are supported now (839) (903)
* `RefM` updates now permit errors (774)
* Supervision, interruptibility & other regional effects are now inherited by child fibers on fork (811) (897)
* Supervision API:
- renamed `supervise` to `interruptChildren`
- renamed `superviseWith` to `handleChildrenWith`
- Added `unsupervised`
* Other API changes:
- `effectTotalWith` has been superseded by `suspendWith` (863)
- Added `tapError` (864)
- Added `ZIO.foreach_`, `ZIO.foreachPar_`, `ZIO.foreachParN_` (781)
- `ensuringR` is replaced by `ensuring` (769)
- `Blocking`, `Scheduler` & `Clock` `Live` traits no longer allocate new thread pools on inheritance (845) (876)
ZIO Interop
* Added cats-effect interop layer for `ZManaged`, conversions to/from cats `Resource` and instances for `Monad, `MonadError`, `Monoid` & `SemigroupK` (827)
* Added cats-effect compatible STM wrappers: `STM`, `TRef`, `TSemaphore`, `TPromise`, `TQueue` (814) (796)
* Added interop module for Twitter futures (833)
* Added `unsafeRunToTwitterFuture` (882)
**Release notes courtesy of kaishh, with help from iravid**