Make JavaScript client work in both Node.js and browser

* Replace jQuery with SuperAgent which works in both Node.js and browser
* Use UMD pattern (returnExports.js) to make the module exporting compatible
  with all major systems: AMD, Node.js (CommonJS) and browser
* Implement support of header and form parameters. Closes #1736
* Move HTTP requesting code to `ApiClient` and allow customizing options
  in it, e.g. "basePath"
* Update unit tests accordingly and add some tests for `ApiClient`

samples/client/petstore/javascript/test/ApiClientTest.js

@@ -0,0 +1,69 @@
+if (typeof module === 'object' && module.exports) {
+  var expect = require('expect.js');
+  var SwaggerPetstore = require('../src/index');
+}
+
+var apiClient = SwaggerPetstore.ApiClient.default;
+
+describe('ApiClient', function() {
+  describe('defaults', function() {
+    it('should have correct default values with the default API client', function() {
+      expect(apiClient).to.be.ok();
+      expect(apiClient.basePath).to.be('http://petstore.swagger.io/v2');
+    });
+
+    it('should have correct default values with new API client and can customize it', function() {
+      var newClient = new SwaggerPetstore.ApiClient;
+      expect(newClient.basePath).to.be('http://petstore.swagger.io/v2');
+      expect(newClient.buildUrl('/abc', {})).to.be('http://petstore.swagger.io/v2/abc');
+
+      newClient.basePath = 'http://example.com';
+      expect(newClient.basePath).to.be('http://example.com');
+      expect(newClient.buildUrl('/abc', {})).to.be('http://example.com/abc');
+    });
+  });
+
+  describe('#paramToString', function() {
+    it('should return empty string for null and undefined', function() {
+      expect(apiClient.paramToString(null)).to.be('');
+      expect(apiClient.paramToString(undefined)).to.be('');
+    });
+
+    it('should return string', function() {
+      expect(apiClient.paramToString('')).to.be('');
+      expect(apiClient.paramToString('abc')).to.be('abc');
+      expect(apiClient.paramToString(123)).to.be('123');
+    });
+  });
+
+  describe('#buildUrl', function() {
+    it('should work without path parameters in the path', function() {
+      expect(apiClient.buildUrl('/abc', {})).to
+        .be('http://petstore.swagger.io/v2/abc');
+      expect(apiClient.buildUrl('/abc/def?ok', {id: 123})).to
+        .be('http://petstore.swagger.io/v2/abc/def?ok');
+    });
+
+    it('should work with path parameters in the path', function() {
+      expect(apiClient.buildUrl('/{id}', {id: 123})).to
+        .be('http://petstore.swagger.io/v2/123');
+      expect(apiClient.buildUrl('/abc/{id}/{name}?ok', {id: 456, name: 'a b'})).to.
+        be('http://petstore.swagger.io/v2/abc/456/a%20b?ok');
+    });
+  });
+
+  describe('#isJsonMime', function() {
+    it('should return true for JSON MIME', function() {
+      expect(apiClient.isJsonMime('application/json')).to.be(true);
+      expect(apiClient.isJsonMime('application/json; charset=UTF8')).to.be(true);
+      expect(apiClient.isJsonMime('APPLICATION/JSON')).to.be(true);
+    });
+
+    it('should return false for non-JSON MIME', function() {
+      expect(apiClient.isJsonMime('')).to.be(false);
+      expect(apiClient.isJsonMime('text/plain')).to.be(false);
+      expect(apiClient.isJsonMime('application/xml')).to.be(false);
+      expect(apiClient.isJsonMime('application/jsonp')).to.be(false);
+    });
+  });
+});