Merges JWS (JSON Web Signature) support.

Authored by Patrizio Bruno <desertconsulting@gmail.com>

note: I usually don't squash commits but I had to significantly re-work
the pull request and squashing was the only reasonable solution. The
commit history as well as the discussion is avaiable at:
#15

The main difference between the PR and this code are:
* jose-jwe-utils.js was renamed to jose-utils.js
* the Gruntfile was fixed to pass Travis build.
* style changes to jose-jwe-decrypt.js and jost-jwe-encrypt.js were
  rejected.
* `var that = this` constructs were rejected.
* alg is a required parameter for importRsaPublicKey and importRsaPrivateKey.
* isCryptoKey was added to the Utils namespace.

(in diff format: https://gist.github.com/alokmenghrajani/eb7fe614402d3723a451)

Gruntfile.js

@@ -8,34 +8,52 @@ module.exports = function(grunt) {
     },
 
     concat: {
-      dist: {
+      prod: {
+        options: {
+          banner: '(function(exports, crypto, Promise, Error, Uint8Array){\n"use strict";\n\n// supporting Safari and its vendor prefix\nif(!crypto.subtle) crypto.subtle = crypto.webkitSubtle;\n',
+          footer: "}(window, window.crypto, window.Promise, window.Error, window.Uint8Array));\n"
+        },
+        src: [
+          'lib/jose-core.js',
+          'lib/jose-jwe-webcryptographer.js',
+          'lib/jose-utils.js',
+          'lib/jose-jwe-encrypt.js',
+          'lib/jose-jwe-decrypt.js',
+          'lib/jose-jws-sign.js',
+          'lib/jose-jws-verify.js'
+        ],
+        dest: 'dist/jose.js'
+      },
+      testing: {
         options: {
-          banner: "(function(){\n",
-          footer: "}());\n"
+          banner: '(function(exports, crypto, Promise, Error, Uint8Array){\n// supporting Safari and its vendor prefix\nif(!crypto.subtle) crypto.subtle = crypto.webkitSubtle;\n',
+          footer: "}(window, window.crypto, window.Promise, window.Error, window.Uint8Array));\n"
         },
         src: [
-          'lib/jose-jwe-core.js',
+          'lib/jose-core.js',
           'lib/jose-jwe-webcryptographer.js',
-          'lib/jose-jwe-utils.js',
+          'lib/jose-utils.js',
           'lib/jose-jwe-encrypt.js',
           'lib/jose-jwe-decrypt.js',
+          'lib/jose-jws-sign.js',
+          'lib/jose-jws-verify.js'
         ],
-        dest: 'dist/jose-jwe.js'
+        dest: 'dist/jose-testing.js'
       }
     },
 
     uglify: {
       dist: {
-        src: 'dist/jose-jwe.js',
-        dest: 'dist/jose-jwe.min.js'
+        src: 'dist/jose.js',
+        dest: 'dist/jose.min.js'
       }
     },
 
     karma: {
       with_coverage: {
         options: {
           preprocessors: {
-            'dist/jose-jwe.js': ['coverage']
+            'dist/jose-testing.js': ['coverage']
           },
           reporters: ['coverage'],
           coverageReporter: {
@@ -44,7 +62,7 @@ module.exports = function(grunt) {
           },
           frameworks: ['qunit'],
           files: [
-            {pattern: 'dist/jose-jwe.js', watching: false, included: false},
+            {pattern: 'dist/jose-testing.js', watching: false, included: false},
             {pattern: 'test/qunit-promises.js', watching: false, included: false},
             'test/jose-jwe-test.html'
           ],
@@ -64,9 +82,10 @@ module.exports = function(grunt) {
         options: {
           frameworks: ['qunit'],
           files: [
-            {pattern: 'dist/jose-jwe.js', watching: false, included: false},
+            {pattern: 'dist/jose-testing.js', watching: false, included: false},
             {pattern: 'test/qunit-promises.js', watching: false, included: false},
-            'test/jose-jwe-test.html'
+            'test/jose-jwe-test.html',
+            'test/jose-jws-test.html'
           ],
           autoWatch: true,
           browsers: ['Chrome'],
@@ -91,7 +110,7 @@ module.exports = function(grunt) {
     }
   };
 
-  if(process.env.TRAVIS){
+  if (process.env.TRAVIS) {
     config.karma.with_coverage.browsers = ['Chrome_travis_ci'];
     config.karma.without_coverage.browsers = ['Chrome_travis_ci'];
   }