value-pairs: Silence a few compiler warnings

Avoid signed-unsigned comparsions, and silence a few other warnings too.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Merge pull request #128 from algernon/h/value-pairs/warning-fixes

value-pairs: Silence a few compiler warnings
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>