Updated NEWS and appveyor files

Merge pull request tpaviot#650 from tpaviot/review/prepare-0.18

Review/prepare 0.18

Updated REAMDE.md for 0.17.2

Merge pull request tpaviot#597 from tpaviot/tp/prepare-release-0.17.1

Prepare release 0.17.1

Import of OCCT 6.8.0

OCE 0.17 released

Merge pull request tpaviot#543 from tpaviot/review/prepare-0.16.1

review/prepare 0.16.1

Import of OCCT 6.7.1

OCE 0.16 released

OCE 0.15 released