Move all Dataset functionality under the Miso.Dataset namespace

[iros]

What should the remappings be:

Here are some suggested ones. What do you think?

Miso.Builder      -> Miso.Dataset.Builder
Miso.Column     -> Miso.Dataset.Column
Miso.DataView  -> Miso.Dataset.View
Miso.Derived     -> Miso.Dataset.Derived
Miso.Event        -> Miso.Dataset.Event
Miso.Events      -> Miso.Dataset.Events
Miso.Importers  -> Miso.Dataset.Importers
Miso.Parsers    -> Miso.Dataset.Parsers
Miso.Product    -> Miso.Dataset.Product
Miso.types       -> Miso.Dataset.Types
Miso.typeOf     -> Miso.Dataset.Types.typeof

Not sure about this one... it is a generic Xhr implementation that is independent of Dataset... Miso.Xhr -> ?

This does make our importers and parsers rather long: Miso.Dataset.Parsers.Delimited Is that too long? I worry that it might be.

[iros]

Fixed in commit 1cf177be491192c7c9f931e05add50ce925faa83