Hook up ESLint, fix warnings (including conversion to async I/O).

lib/markdownlint.js

@@ -3,25 +3,42 @@
 var fs = require("fs");
 var rules = require("./rules");
 
-function lintFile(file, options) {
-  var results = {};
-  var contents = fs.readFileSync(file, { encoding: "utf8" });
-  var lines = contents.split(/\r\n|\n/g);
-  Object.keys(rules).forEach(function(name) {
-    var rule = rules[name];
-    var errors = rule(lines);
-    if (errors.length) {
-      results[name] = errors;
+function lintFile(file, options, callback) {
+  fs.readFile(file, { "encoding": "utf8" }, function readFile(err, contents) {
+    if (err) {
+      callback(err);
+    } else {
+      var lines = contents.split(/\r\n|\n/g);
+      var result = {};
+      Object.keys(rules).forEach(function forRule(name) {
+        var rule = rules[name];
+        var errors = rule(lines);
+        if (errors.length) {
+          result[name] = errors;
+        }
+      });
+      callback(null, result);
     }
   });
-  return results;
 }
 
-module.exports = function(options) {
+module.exports = function markdownlint(options, callback) {
   var results = {};
   var files = options.files || [];
-  files.forEach(function(file) {
-    results[file] = lintFile(file, options);
-  });
-  return results;
+  function lintFiles() {
+    var file = files.shift();
+    if (file) {
+      lintFile(file, options, function lintFileCallback(err, result) {
+        if (err) {
+          callback(err);
+        } else {
+          results[file] = result;
+          lintFiles();
+        }
+      });
+    } else {
+      callback(null, results);
+    }
+  }
+  lintFiles();
 };

lib/rules.js

@@ -3,20 +3,20 @@
 function padAndTrim(lines) {
   return [].concat(
     "",
-    lines.map(function(line) {
+    lines.map(function mapLine(line) {
       return line.trim();
     }),
     "");
 }
 
 module.exports = {
-  MD031: function(lines) {
+  "MD031": function MD031(lines) {
     // Some parsers have trouble detecting fenced code blocks without
     // surrounding whitespace, so examine the lines directly.
     lines = padAndTrim(lines);
     var errors = [];
     var inCode = false;
-    lines.forEach(function(line, lineNum) {
+    lines.forEach(function forLine(line, lineNum) {
       if (line.match(/^(```|~~~)/)) {
         inCode = !inCode;
         if ((inCode && lines[lineNum - 1].length) ||