Merge branch 'feature/regularize-truncated-diagonal' into 'master'

Add support for regularizing truncated diagonal entries

See merge request !26
4 jobs for master in 14 minutes and 25 seconds (queued for 7 seconds)
Status Name Job ID Coverage
  Test
passed dune:git clang C++17 #169771

00:04:29

passed dune:git clang C++17 with examples #169773

00:07:42

passed dune:git gcc-8 C++17 #169772

00:07:17

passed dune:git gcc-8 C++17 with examples #169774

00:09:55