move docs to folder

doc/modules.md

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+# Modules
+
+## Usage
+
+### CLI
+
+    $ 6to5 --modules common script.js
+
+### Node
+
+```javascript
+var to5 = require("6to5");
+to5.transform('import "foo";', { modules: "common" });
+```
+
+## Formats
+
+### Common (Default)
+
+**In**
+
+```javascript
+import "foo";
+
+import foo from "foo";
+import * as foo from "foo";
+
+import {bar} from "foo";
+import {foo as bar} from "foo";
+
+export {test};
+export var test = 5;
+
+export default test;
+```
+
+**Out**
+
+```javascript
+require("foo");
+
+var foo = require("foo").default;
+var foo = require("foo");
+
+var bar = require("foo").bar;
+var bar = require("foo").foo;
+
+exports.test = test;
+var test = 5; exports.test = test;
+
+exports.default = test;
+```
+
+### AMD
+
+**In**
+
+```javascript
+import foo from "foo";
+
+export function bar() {
+  return foo("foobar");
+}
+```
+
+**Out**
+
+```javascript
+define(["exports", "foo"], function (exports, _foo) {
+  exports.bar = bar;
+
+  var foo = _foo.default;
+
+  function bar() {
+    return foo("foobar");
+  }
+});
+```
+
+### UMD
+
+**In**
+
+```javascript
+import foo from "foo";
+
+export function bar() {
+  return foo("foobar");
+}
+```
+
+**Out**
+
+```javascript
+(function (factory) {
+  if (typeof define === "function" && define.amd) {
+    define(["exports", "foo"], factory);
+  } else if (typeof exports !== "undefined") {
+    factory(exports, require("foo"));
+  }
+})(function (exports) {
+  exports.bar = bar;
+
+  var foo = _foo.default;
+
+  function bar() {
+    return foo("foobar");
+  }
+});
+```
+
+### Ignore
+
+
+**In**
+
+```javascript
+import foo from "foo";
+
+export function bar() {
+  return foo("foobar");
+}
+```
+
+**Out**
+
+```javascript
+function bar() {
+  return foo("foobar");
+}
+```
+
+## Custom
+
+You can alternatively specify module names instead of one of the built-in types.
+
+    $ 6to5 --modules custom-module-formatter
+
+**node_modules/custom-module-formatter/index.js**
+
+```javascript
+module.exports = ModuleFormatter;
+
+function ModuleFormatter() {
+
+}
+
+ModuleFormatter.prototype.transform = function (ast) {
+  // this is ran after all transformers have had their turn at modifying the ast
+  // feel free to modify this however
+};
+
+ModuleFormatter.prototype.import = function (node, nodes) {
+  // node is an ImportDeclaration
+};
+
+ModuleFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
+  // specifier is an ImportSpecifier
+  // node is an ImportDeclaration
+};
+
+ModuleFormatter.prototype.export = function (node, nodes) {
+  // node is an ExportDeclaration
+};
+
+ModuleFormatter.prototype.exportSpecifier = function (specifier, node, nodes) {
+  // specifier is an ExportSpecifier
+  // node is an ExportDeclaration
+};
+```