Add brief headers to new files

injector.js

@@ -1,5 +1,7 @@
 const injector = {};
 
+// These functions are used to actually inject the instrumentation events.
+
 injector.callEvent = function injectCallEvent(contract, fileName, injectionPoint) {
   const linecount = (contract.instrumented.slice(0, injectionPoint).match(/\n/g) || []).length + 1;
   contract.runnableLines.push(linecount);

instrumenter.js

@@ -1,5 +1,8 @@
 const instrumenter = {};
 
+// These functions work out where in an expression we can inject our
+// instrumenation events.
+
 function createOrAppendInjectionPoint(contract, key, value) {
   if (contract.injectionPoints[key]) {
     contract.injectionPoints[key].push(value);

parse.js

@@ -1,6 +1,9 @@
 const parse = {};
 const instrumenter = require('./instrumenter');
 
+// All the functions in this file do is walk the AST and call the instrumenter
+// functions where appropriate, which determine where to inject events.
+
 // Assign a dummy function to everything we might see in the AST
 ['AssignmentExpression',
   'BinaryExpression',