Add RC3 blog article

Author: anatoliykmetyuk

docs/blog/_posts/2021-04-21-scala3-rc3.md

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+---
+layout: blog-page
+title: Scala 3.0.0-RC3 – bug fixes for 3.0.0 stable
+author: Anatolii Kmetiuk
+authorImg: /images/anatolii.png
+date: 2021-04-21
+---
+
+Hello! With this blog article, we would like to announce the release of Scala 3.0.0-RC3. Some critical bugs were discovered during the previous release cycle the fixes to which had to be included in 3.0.0 stable. Therefore, we are having RC3 to give the community time to test our fixes.
+
+This release also impacts the release date for 3.0.0 stable. 3.0.0 stable will get a green light if no critical bugs are discovered until May 12th. Otherwise we may need to have an RC4.
+
+<!--more-->
+
+# Bug fixes included
+- Backport: Fix type test for trait parameter arguments [#12066](https://github.com/lampepfl/dotty/pull/12066)
+- Backport: Set file filter correctly [#12119](https://github.com/lampepfl/dotty/pull/12119)
+- Backport: Provide mirror support after inlining [#12079](https://github.com/lampepfl/dotty/pull/12079)
+- Fix type test for trait parameter arguments [#12064](https://github.com/lampepfl/dotty/pull/12064)
+- Backport: Revert "Recursively check nonvariant arguments of base types for realizability" [#12067](https://github.com/lampepfl/dotty/pull/12067)
+- Backport: When simplifying match types, ensure fully defined before reducing [#12068](https://github.com/lampepfl/dotty/pull/12068)
+- Backport: sbt-dotty: the binary version is 3 for Scala >= 3.0.0 [#12084](https://github.com/lampepfl/dotty/pull/12084)
+- Backport: Fix isInstanceOf[Array[?]] returning true on non-Array [#12108](https://github.com/lampepfl/dotty/pull/12108)
+- Backport: Scala2Unpickler: don't unpickle the same type parameter twice [#12129](https://github.com/lampepfl/dotty/pull/12129)
+- [Backport] Overloading resolution: Handle SAM types more like Java and Scala 2 [#12131](https://github.com/lampepfl/dotty/pull/12131)
+- Add TermParamClause.isGiven [#12042](https://github.com/lampepfl/dotty/pull/12042)
+
+## Contributors
+Thank you to all the contributors who made this release possible 🎉
+
+According to `git shortlog -sn --no-merges 3.0.0-RC2..3.0.0-RC3` these are:
+
+```
+     8  Martin Odersky
+     7  Adrien Piquerez
+     6  Guillaume Martres
+     4  Liu Fengyun
+     1  Anatolii Kmetiuk
+     1  Nicolas Stucki
+```
+
+If you want to get your hands dirty and contribute to Dotty, now is a good time to get involved!
+Head to our [Getting Started page for new contributors](https://dotty.epfl.ch/docs/contributing/getting-started.html),
+and have a look at some of the [good first issues](https://github.com/lampepfl/dotty/issues?q=is%3Aissue+is%3Aopen+label%3Aexp%3Anovice).
+They make perfect entry points into hacking on the compiler.
+
+We are looking forward to having you join the team of contributors.
+
+## Library authors: Join our community build
+
+Dotty now has a set of widely-used community libraries that are built against every nightly Dotty
+snapshot. Currently, this includes shapeless, ScalaPB, algebra, scalatest, scopt and squants.
+Join our [community build](https://github.com/lampepfl/dotty/tree/master/community-build)
+to make sure that our regression suite includes your library.
+
+[Scastie]: https://scastie.scala-lang.org/?target=dotty
+
+[@odersky]: https://github.com/odersky
+[@DarkDimius]: https://github.com/DarkDimius
+[@smarter]: https://github.com/smarter
+[@felixmulder]: https://github.com/felixmulder
+[@nicolasstucki]: https://github.com/nicolasstucki
+[@liufengyun]: https://github.com/liufengyun
+[@OlivierBlanvillain]: https://github.com/OlivierBlanvillain
+[@biboudis]: https://github.com/biboudis
+[@allanrenucci]: https://github.com/allanrenucci
+[@Blaisorblade]: https://github.com/Blaisorblade
+[@Duhemm]: https://github.com/Duhemm
+[@AleksanderBG]: https://github.com/AleksanderBG
+[@milessabin]: https://github.com/milessabin
+[@anatoliykmetyuk]: https://github.com/anatoliykmetyuk