Add 'forEachPar' and 'forEachSeq' helpers to promise helper module.

These factor out common patterns.

Change-Id: I2d757de38120f41b8ba7178e80888b42cf7e7c7f
Add featured article list and a script to build collections from it.

Change-Id: Ib1f56a103c233cbde54ea63d3885a1fbb567a7ea