Umbrella strategies.#726

Merged

awulkiew merged 3 commits intoboostorg:developfrom

awulkiew:feature/strategies

Aug 28, 2020

Commits on Jul 10, 2020

[algorithms][strategies] Add umbrella strategies for area, envelope and expand.
awulkiew
committed

Commits on Aug 5, 2020

[strategies] Relocate area, envelope and expand strategies.
awulkiew
committed

Commits on Aug 11, 2020

[gh] Remove unsupported compilers/standards from GH workflows.
awulkiew
committed