Crystal 0.20.4 has been released!

As any release it includes numerous bugfixes, cool features and performance improvements - in 87 commits since 0.20.3.

Exciting Changes

(breaking change) YAML::Emitter was renamed to YAML::Builder, and some of its methods were also renamed. It can now used for any YAML serialization using YAML.build.
(breaking change) to_json methods now receives a JSON::Builder instead of an IO. It can now used for any YAML serialization using JSON.build. If you are using JSON.mapping then your code will continue to work without changes.
XML::Builder allows to serialize XML format using XML.build.
(breaking change)MemoryIO was removed in favour of IO::Memory.
with ... yield now works well with method_missing.
Class variables can now be used in generic types (all generic instances share the same variable, and subclasses get their own copy, as usual).
Added support for LLVM 4.

Other Breaking Changes

(breaking change) Defining a finalize method on a struct now gives a compile error
(breaking change) Default argument types now must match their restriction, if any (for example def foo(x : Int32 = nil) will now fail to compile if foo is invoked without arguments) (thanks @MakeNowJust)
(breaking change) each methods now return Nil
(breaking change) IO#skip(bytes) will now raise if there aren’t at least the given amount of bytes in the IO (previously it would work well if there were less bytes, and it would hang if there were more)
(breaking change) Number#step now requires named arguments, to and by, to avoid argument order confusion
(breaking change) XML::Node#[] now always returns a String (previously it could also return Nil, which was incorrect)
(breaking change) XML::Node#content now returns an empty String when no content is available

Thanks to everyone who supported this release through contributions, reviews and suggestions.