#4 Add an IsValid() function to MDObject

[Matt Beard]

This would validate the contents of an MDObject.

The min and max length would be validated.

A new MDTrait call would probably be required to
validate the data as well - types such as integers
would always flag as valid here (the size check would
be done before calling the trait). TimeStamp could
check for Month != 0 and Month < 13 etc.

If an MDObject was a container it would validate all
children.

Please feel free to add comments to this proposal.