Move each rule implementation into its own file (fixes #83).

lib/md037.js

@@ -0,0 +1,29 @@
+// @ts-check
+
+"use strict";
+
+var shared = require("./shared");
+
+module.exports = {
+  "names": [ "MD037", "no-space-in-emphasis" ],
+  "description": "Spaces inside emphasis markers",
+  "tags": [ "whitespace", "emphasis" ],
+  "function": function MD037(params, onError) {
+    shared.forEachInlineChild(params, "text", function forToken(token) {
+      var left = true;
+      var match = /\s(\*\*?|__?)\s.+\1/.exec(token.content);
+      if (!match) {
+        left = false;
+        match = /(\*\*?|__?).+\s\1\s/.exec(token.content);
+      }
+      if (match) {
+        var text = match[0].trim();
+        var line = params.lines[token.lineNumber - 1];
+        var column = line.indexOf(text) + 1;
+        var length = text.length;
+        shared.addErrorContext(onError, token.lineNumber,
+          text, left, !left, [ column, length ]);
+      }
+    });
+  }
+};