create taxon element to contain taxon-name and other elements

[tcatapano]

e.g., taxon-name, taxon-authority, taxon-status, secundum etc...

[teodorgeorgiev]

<nomenclature>
<tp:taxon>
	<tp:taxon-name>
		<tp:taxon-name-part taxon-name-part-type="genus" reg="Eutrema">Eutrema</tp:taxon-name-part>
		<tp:taxon-name-part taxon-name-part-type="species" reg="sinense">sinense</tp:taxon-name-part>
		<object-id content-type="ipni" xlink:type="simple">urn:lsid:ipni.org:names:77190124-1</object-id>
	</tp:taxon-name>
	<tp:taxon-authority>(Hemsl.) G.Q.Hao, J.Quan Liu & Al-Shehbaz</tp:taxon-authority>,
	<tp:taxon-status>comb. nov.</tp:taxon-status>
</tp:taxon>
<tp:taxon role="basionym">
	Based on 
	<tp:taxon-name>
		<tp:taxon-name-part taxon-name-part-type="genus" reg="Braya">Braya</tp:taxon-name-part>
		<tp:taxon-name-part taxon-name-part-type="species" reg="sinensis">sinensis</tp:taxon-name-part>
	</tp:taxon-name>
	<tp:taxon-authority>Hemsl.</tp:taxon-authority>,
 	<xref>J. Linn. Soc., Bot. 30: 303. 1892.</xref>
</tp:taxon>
</nomenclature>

[tcatapano]

add taxon element to taxon-name, material-citation and descriptive-statement as globally available elements. This will be backwards compatible and offer an option rather than require one use or other.

[tcatapano]

Not clear on the status of this request and whether it should be implemented. Removing from milestone 1.0

[gsautter]

Most likely most relevant for botany, where treatments are more likely to have the original protolog citation included in the nomenclature section ... the example from @teodorgeorgiev above should make it pretty clear.