Schema/document fixes so far

I've almost got the initial set of PRD3 schemas to validate
against the sample instances.  Here are the changes I seem to have
needed to make far.  Note that this does not include resolution of
the truncation and abbreviation issues raised by Mike.

Jon

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Changes to first set of schemas (5 September):

1. Change 

      <xsd:import namespace="urn:oasis:names:specification:ubl:schema:xsd:CommonExtensionComponents-2" schemaLocation="../common/UBL-ExtensionContentDatatype-2.0.xsd"/>

   to

     <xsd:import namespace="urn:oasis:names:specification:ubl:schema:xsd:CommonExtensionComponents-2" schemaLocation="../common/UBL-CommonExtensionComponents-2.0.xsd"/>

2. Change all UUIDID to UUID

3. Change all URIID to URI

4. Make all UBLVersionID optional

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Changes to PRD2 sample instances:

 - Change all SubTotal to Subtotal

 - Change all SubsetID to CustomizeID

We still need a change of LegalTotal to various forms of
MonetaryTotal.