type-hinting: Add support for double(...) type hints

This add support for double(...) type hints, to type-hinting only. None
of the drivers were updated to use it yet.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
mongodb: Add support for double() type hints

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
format-json: Add support for double() type hints

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Merge pull request #130 from algernon/f/type-hinting/double

type-hinting: Support double()