added show-top / -bottom options to participants

gallery/example3.typ

@@ -133,4 +133,15 @@ chronos.diagram({
   _seq("a", "a", end-tip: ("o", "//"), comment: `-//o`)
   _seq("a", "a", start-tip: "x", end-tip: ("o", ">"), comment: `x->o`)
 })
-)
+)
+
+#chronos.diagram({
+  import chronos: *
+
+  _par("a", display-name: "Alice")
+  _par("b", display-name: "Bob", show-bottom: false)
+  _par("c", display-name: "Caleb", show-top: false)
+  _par("d", display-name: "Danny", show-bottom: false, show-top: false)
+
+  _gap()
+})