Describe changes from #27

Fixes #53

lang/spec.html

@@ -5444,6 +5444,14 @@ <h3>Summary of changes from 0.990 to 2019r1</h3>
 respectively.</li>
 <li>In the argument list of a function or method call, positional arguments are
 now required to be specified before named arguments.</li>
+<li>Providing a default value for a parameter no longer affects whether a function
+call must supply the argument for that parameter positionally or by name. Instead
+the argument for any parameter can be supplied either positionally or by name.
+To avoid ambiguity, all arguments specified positionally must be specified before
+arguments specified by name.</li>
+<li>Expressions specifying the default value for function parameters are not
+compile time constants, and are evaluated each time they are used to supply a
+missing argument.</li>
 </ol>
 <h3>Summary of changes from 0.980 to 0.990</h3>
 <p>