Log Message:
(math/R-igraph) Updated 1.4.3 to 1.5.0

# igraph 1.5.0

## Breaking changes

The internal format of graph objects has changed in a mostly
backward-compatible way, to prepare for upgrading the C core to
0.10. Details are described at
<https://github.com/igraph/rigraph/wiki/The-igraph-object-format>. Accessing
graph objects that have been created with an older igraph version give
a clean error message with instructions (#832). The new format cannot
be read by igraph 1.4.3 or older, the following error is raised when
trying to do so:

```
This graph was created by an old(er) igraph version.
  Call upgrade_graph() on it to use with the current igraph version
  For now we convert it on the fly...
Error in is_directed(object) :
  REAL() can only be applied to a 'numeric', not a 'NULL'
```

The only supported remedy is to upgrade the igraph package to version
1.5.0 or later.

`graph_version()` now returns an integer scalar (#832, #847), `4` as of igraph \ 
1.5.0 (#835).

## Features

- Vertex and edge sequences are converted to numeric vectors when used
  in attributes (#808).

- New `largest_component()` returns the largest connected component
  (#786, @ngmaclaren).

## Bug fixes

  - Fix error message in `make_graph()` when `simplify = ...` is used
    with a non-formula (#834).

## Testing

- Add more tests for `graph_from_literal()` (#826).

- Reenable serialization test and tests for `dyad_census()`, stabilize
  tests (#809, #822, #823).

## Documentation

- The documentation for the R package is now hosted at
  <https://r.igraph.org/> (#780).

- Update `vignette("installation-troubleshooting")`.

- Fix use of deprecated functions in examples, e.g., replace `gsize()`
  by `ecount()` (#827).

- Fix typos in `?eigen_centrality` docs (@JJ).

- Update CONTRIBUTING.md and ORCID information (#791, #774).

- Add DOI to CITATION (#773).

## Internal

- Add data for old igraph versions as constructed objects, and tests (#838).

- Ensure we're always using named indexes to access the internal data structure \ 
(#784).

- Prepare migration to igraph/C 0.10 (#781).

- Update generated interface (#765).