Update version to 0.4.0 and add some text in CHANGELOG.md

Author: fverdugo

CHANGELOG.md

@@ -5,6 +5,31 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+
+## [0.4.0] - unreleased
+
+## Changed
+
+- Major refactoring in `PSparseMatrix` (and in `PVector` in a lesser extent).
+The old code is still available (but deprecated), and can be recovered applying this renaming to your code-base:
+  - `PSparseMatrix -> OldPSparseMatrix`
+  - `psparse! -> old_psparse!`
+  - `pvector! -> old_pvector!`
+  - `trivial_partition -> old_trivial_partition`
+
+- The default parallel sparse matrix format is now split into 4 blocks corresponding to own/ghost columns/rows.
+The previous "monolithic" storage is not implemented anymore for the new version of `PSparseMatrix`, but can be implemented in the new setup if needed.
+
+## Added
+
+- Efficient re-construction of `PSparseMatrix` and `PVector` objects.
+- Functions `assemble` and `consistent` (allocating versions of `assemble!` and `consistent!` with a slightly different
+treatment of the ghost rows).
+- Function `consitent` for `PSparseMatrix`.
+- Functions `repartition` and `repartition!` used to change the data partition of `PSparseMatrix` and `PVector` objects.
+- Functions `psystem` and `psystem!` for generating a system matrix and vector at once.
+- Function `trivial_partition`.
+
 ## [0.3.4] - 2023-09-06
 
 ### Added 

Project.toml

@@ -1,7 +1,7 @@
 name = "PartitionedArrays"
 uuid = "5a9dfac6-5c52-46f7-8278-5e2210713be9"
 authors = ["Francesc Verdugo <f.verdugo.rojano@vu.nl> and contributors"]
-version = "0.3.4"
+version = "0.4.0"
 
 [deps]
 CircularArrays = "7a955b69-7140-5f4e-a0ed-f168c5e2e749"