More sane naming for the variable typing code

More sane naming for the variable typing code

oe.types.value -> oe.data.typed_value

    This name has been bugging me.  This function is the primary interface to
    the module for OE metadata, as it takes a variable name and datastore and
    returns an object of the correct type.  While this function is part of the
    variable typing implementation, in reality it's more about giving you a
    useful object from the metadata, so I think oe.data is a more appropriate
    place for it.

oe.types -> oe.maketype

    These are the functions which construct types, not the types themselves,
    so it was somewhat misleading.

oe._types -> oe.types

    These are the actual types, any callable in this module becomes an OE
    type, using its arguments to determine the variable flags (optional and
    required) to obey.  Will use __init__'s args in the case of an actual
    python class.

Signed-off-by: Chris Larson <chris_larson@mentor.com>