[prakriya] Greatly increase Unadipatha coverage

This commit substantially increases our support for the Unadipatha and
increases the size of our Unadipatha test suite to 500 passing tests. In
addition, I updated some of our documentation and doctests to be more
thorough and accurate.

vidyut-prakriya/README.md

@@ -85,7 +85,8 @@ for p in prakriyas {
     println!("{}", p.text());
     println!("---------------------------");
     for step in p.history() {
-        let result: String = step.result().join(" + ");
+        let terms: Vec<_> = step.result().iter().map(|x| x.text()).filter(|x| !x.is_empty()).collect();
+        let result = terms.join(" + ");
         println!("{:<10} | {}", step.rule().code(), result);
     }
     println!("---------------------------");