Minor changes to fix issues identified by Maciej

The following have been fixed:

1. For MultinomialDistribution, the number of <probabilities> elements
should be unlimited, but in the spec the default (= 1) is used:

<xs:complexType name="MultinomialDistributionType">
<xs:complexContent>
<xs:extension base="un:AbstractDiscreteMultivariateDistributionType">
<xs:sequence>
<xs:element name="numberOfTrials" type="un:NaturalNumberValueType"/>
<xs:element name="probabilities" type="un:ProbabilityValueType"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>

**DC: I agree. Changed.

2. Wishart distribution is a multivariate continuous distribution but
not a discrete one as the spec defines:
(https://en.wikipedia.org/wiki/Wishart_distribution)

<xs:element name="WishartDistribution"
substitutionGroup="un:AbstractDiscreteMultivariateDistribution">
<xs:complexType>
<xs:complexContent>
<xs:extension base="un:WishartDistributionType"/>
</xs:complexContent>
</xs:complexType>
</xs:element>

**DC: Oophs, that slipped through, you are totally correct there.
Changed

3. <DirichletDistribution> allows to define only 1 <concentration> value
so far, but it should allow K (number of categories)

<xs:complexType name="DirichletDistributionType">
<xs:complexContent>
<xs:extension base="un:AbstractContinuousMultivariateDistributionType">
<xs:sequence>
<xs:element name="concentration" type="un:PositiveRealValueType"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>

'maxOccurs="unbounded"' should be additionally specified in
<xs:element name="concentration" type="un:PositiveRealValueType"/>

**DC: Agreed and changed.

5. What is the reason to call the truncation bounds in few cases
"truncationLowerInclusiveBoundIG" or "truncationUpperInclusiveBoundIG"
rather then
"truncationLowerInclusiveBound" or "truncationUpperInclusiveBound"

This is the case for
- ChiSquareDistribution
- FDistribution
For these distributions only one truncation pair is defined so the name
suffix 'IG' is confusing, unless it has a good reason to be called this
way.

**DC: Again, you are correct. This looks like a copy/paste error in
adding the truncation support. Changed