Math helper nearly done, test almost passes.

src/renderer/parameters_context.rs

@@ -68,6 +68,16 @@ impl<'a> ParametersContext<'a> {
         }
     }
 
+    pub fn from_values(
+        parent: Option<&'a ParametersContext<'a>>,
+        params: HashMap<&'a str, Option<BreadcrumbTreeElement<'a>>>,
+    ) -> Self {
+        ParametersContext {
+            parent: parent,
+            params: params,
+        }
+    }
+
     pub fn contains_key(&self, segment: &str) -> bool {
         self.params.contains_key(segment)
             || self