[m2] How to set a Mojo property from settings.xml

[David Jackman]

One of the properties for a Mojo I'm writing is really a user-specific
thing, and ought to be set in each user's settings.xml file.  The guide
for configuring plugins only talks about setting configuration
properties in pom.xml, but not how to reference values set in
settings.xml.  How do I do this?
 
..David..