XTCE13 — Re-evaluate the characterWidth attribute in String types

I am not sure that this attribute makes sense in the String data type definitions. The character encoding (@encoding) element really should capture the knowledge here, but there could be a nuance I am unsure about.

Check on this in the committee meeting. Propose to remove the attribute.

Fix ambiguity with characterWidth attribute

At present, the characterWidth attribute on BOTH the complexType definitions of StringDataType and ArgumentStringDataType is undocumented and as a result not particularly clear. The proposal is to replace the attribute definition of:

<attribute name="characterWidth" type="xtce:CharacterWidthType"/>

With a new definition containing annotation/documentation of:

<attribute name="characterWidth" type="xtce:CharacterWidthType">
<annotation>
<documentation xml:lang="en">Optional hint to the implementation about the size of the engineering/calibrated data type to use internally. Generally this can be determined by examination of the encoding information for the string, but it is not always clear, so this attribute allows the extra hint when needed. A tolerant implementation will endeavor to always make sufficient size engineering data types to capture the entire range of possible characters.</documentation>
</annotation>
</attribute>

Lastly, the simpleType "CharacterWidthType" misses the possibility that a 32 bit character width is used. Propose to change the existing:

<simpleType name="CharacterWidthType">
<restriction base="integer">
<enumeration value="8"/>
<enumeration value="16"/>
</restriction>
</simpleType>

To the following definition by adding a value of 32 to the list:

<simpleType name="CharacterWidthType">
<restriction base="integer">
<enumeration value="8"/>
<enumeration value="16"/>
<enumeration value="32"/>
</restriction>
</simpleType>