* **(breaking change)** `IO#gets`, `IO#each_line`, `String#lines`, `String#each_line`, etc. now chomp lines by default. You can pass `chomp: false` to prevent automatic chomping. Note that `chomp` is `true` by default for argless `IO#gets` (read line) but `false` if args are given.

* **(breaking change)** `HTTP::Handler` is now a module instead of a class (thanks @andrewhamon)

* **(breaking change)** Free variables now must be specified with `forall`, a single uppercase letter will not work anymore

* **(breaking change)** The `libs` directory is no longer in the default CRYSTAL_PATH, use `lib` (running `crystal deps` should fix this)

* Optimized compile times, specially on linux

* `private` can now be used with macros inside types (thanks @MakeNowJust)

* CLI: the `-s`/`--stats` option now also shows execution time (thanks @MakeNowJust)

* CLI: added `-t`/`--time` to show execution time (thanks @MakeNowJust)

* `Socket` now allows any family/type/protocol association, [and many other improvements](https://github.com/crystal-lang/crystal/pull/3750) (thanks @ysbaddaden)

* YAML: an `IO` can now be passed to `from_yaml` (thanks @MakeNowJust)

* Added `class_getter`, `class_setter`, `class_property`, etc. (thanks @Sija)

* Added `String#lchomp` (thanks @Sija)

* Added `IO#read_fully?`

* Added `Iterator#flatten` (thanks @MakeNowJust)

* Added `HTTP::WebSocket#ping`, `pong`, `on_ping`, `on_pong`, and now a ping message is automatically replied with a pong message (thanks @Sija)

* Added `File#empty?` and `Dir#empty?` (thanks @dylandrop)

* Added `Time::Span#/(Time::Span)` (thanks @RX14)

* Added `String#split` versions that accept a block (thanks @splattael)

* Added `URI#normalize` and `normalize!` (thanks @taylorfinnell)

* Added `reuse` optional argument to many `Array`, `Enumerable` and `Iterable` methods that allow you to reuse the yielded/return array for better performance and less memory footprint

* The `:debug` flag is now present when compiled with `--debug`, useful for doing `flag?(:debug)` in macros (thanks @luislavena)

* [Many bug fixes and performance improvements](https://github.com/crystal-lang/crystal/issues?q=is%3Aclosed+milestone%3A0.20.2)