[ARTS-2.6] Bump version to 2.6.18 (#1052)

Bump version to 3.0.0dev8 (#1040)

[ARTS-2.6] Bump version to 2.6.16 (#972)

[ARTS-2.6] Bump version to 2.6.14 (#920)

Bump version to 3.0.0dev6 (#877)

[ARTS-2.6] Bump version to 2.6.12 (#876)

Bump version to 3.0.0dev4 (#871)

Bump version to 3.0.0dev2 (#844)

For snapshot release.

[ARTS-2.6] Bump version to 2.6.10 (#841)

[ARTS-2.6] Bump version to 2.6.8 (#825)