[Headercheck] Fix headercheck by adding missing static_assert.hh includes.
[Documentation] Fix typo in argument documentation.
[Dependencies] Bump dune-common minimum version requirement to 2.3.1
[Documentation] Update release notes and bump version to 2.3.1-rc1

We'll skip 2.3.0 and go directly to 2.3.1 for uniformity with the core
modules.
[Release] Update version information for 2.3.1
Merge branch 'releases/2.3'

Pull in fixes from release branch

* releases/2.3:
  [Release] Update version information for 2.3.1
  [Documentation] Update release notes and bump version to 2.3.1-rc1
  [Dependencies] Bump dune-common minimum version requirement to 2.3.1
  [Documentation] Fix typo in argument documentation.
  [Headercheck] Fix headercheck by adding missing static_assert.hh includes.

Conflicts:
	README
	dune.module
	dune/typetree/filteredcompositenode.hh
	dune/typetree/filters.hh
	dune/typetree/variadiccompositenode.hh