allow <valList> as child of macroSpec

If you want a make a macro which defines a set of fixed choices, the TEI <valList> is a more natural tool than plain RNG, allowing as it does for the documentation desc/gloss elements. However, <macroSpec> does not permit use of <valList>.

I propose that the content model of macroSpec be changed to .. <rng:zeroOrMore>
<rng:choice>
<rng:ref name="stringVal"/>
<rng:ref name="content"/>
<rng:ref name="valList"/>
</rng:choice>
</rng:zeroOrMore>

... to allow macro content models to be closer to element content models.

data.sex is an example of a macro which would benefit