Allow partial imports (#125)

`this.parse(this.extract(str), opts)` assumes `query-string` will always be imported fully. Importing `stringify` by itself works, but not `parseUrl`. This change makes the `parseUrl` export independent, allowing `import { parseUrl } from 'query-string'` and a more consistent behavior.

index.js

@@ -113,15 +113,15 @@ function keysSorter(input) {
  return input;
 }
 
-exports.extract = function (str) {
+function extract(str) {
  var queryStart = str.indexOf('?');
  if (queryStart === -1) {
  return '';
  }
  return str.slice(queryStart + 1);
-};
+}
 
-exports.parse = function (str, opts) {
+function parse(str, opts) {
  opts = objectAssign({arrayFormat: 'none'}, opts);
 
  var formatter = parserForArrayFormat(opts);
@@ -165,7 +165,10 @@ exports.parse = function (str, opts) {
 
  return result;
  }, Object.create(null));
-};
+}
+
+exports.extract = extract;
+exports.parse = parse;
 
 exports.stringify = function (obj, opts) {
  var defaults = {
@@ -216,6 +219,6 @@ exports.stringify = function (obj, opts) {
 exports.parseUrl = function (str, opts) {
  return {
  url: str.split('?')[0] || '',
- query: this.parse(this.extract(str), opts)
+ query: parse(extract(str), opts)
  };
 };