igraph 2.0.3

See https://github.com/igraph/rigraph/blob/3299d31/src/vendor/cigraph/CHANGELOG.md for a complete changelog of the bundled C core, and https://github.com/igraph/rigraph/compare/f3fa58b..3299d31#diff-aeb78e0159780a9b26daabaf6f95f450b0cfec7161fc735f27ad69145a57dc84 for the changes since the igraph 2.0.1.
(A permanent link to the most recent changelog of the C core used in the R package is
https://github.com/igraph/rigraph/blob/main/src/vendor/cigraph/CHANGELOG.md.)

Features

• GMP is no longer a dependency (#1256), libxml2 (#1282) and glpk are optional.
• Update vendored sources to igraph/igraph@857a125.
• New voronoi_cells() to compute the Voronoi partitioning of a graph (#1173).

Bug fixes

• Fix rglplot(edge_label = ) (#1267).

Continuous integration

• Run examples with sanitizer (#1288).
• Add scheduled builds.

Documentation

• Make x11() usage in example happen only in interactive sessions (#1301).
• Remove misleading comment about warning given as no warning is given (#1294).
• Improve min_st_separators() documentation (#1264).
• Add link to discussion forum (#1279) and logo (#1280).
• Add code finding duplicate @seealso, and use it (#1270).
• Remove duplicate @seealso from ?sample_pa (#1268).
• Remove incorrect claim about handling of complete graphs by is_separator() and is_min_separator() (#1263).
• Fix error messages mentioning to mention upgrade_graph() instead of the nonexisting upgrade_version() (#1252).
• Split is_bipartite() manual page from other manual page (#1230).
• Improve bug report template.
• CITATION.cff contains only the first three version components.
• Install lock workflow to lock stale discussions after one year (#1304).

Internal

• Replace use of deprecated barabasi.game() with sample_pa() (#1291).
• Auto-generate are_adjacent(), avoid deprecated igraph_are_connected() C function (#1254).