[expand] Add variant support
Merge remote-tracking branch 'boostorg/geometry/develop' into variant/expand
[expand] Add tests for variant
[expand] Adds support for variant box
Revert "[expand] Adds support for variant box"

This reverts commit 52ce484c7f61c5931f6392ba456c31fdabed4a06.
[expand] Move concept check
Merge pull request #39 from sdebionne/variant/expand

[expand] Add variant support