Move then and resolve to interop section

[briancavalier]

See #179

Move docs for .then and resolve to a new section specifically for P/A+ and ES Promise interop. Move map to first in the "Transform" section. Add "Flow control" heading for catch and finally.

[coveralls]

Coverage remained the same at 100.0% when pulling d5ec636 on reorg-api-docs-es-aplus into b124e6f on master.

[coveralls]

Coverage remained the same at 100.0% when pulling d5ec636 on reorg-api-docs-es-aplus into b124e6f on master.

[coveralls]

Coverage remained the same at 100.0% when pulling d5ec636 on reorg-api-docs-es-aplus into b124e6f on master.