feature(extensionLoading): add support to legacy extensions in the ne…

…w extension mechanism

Old extensions that register themselves in `showdown.extensions` can be loaded and validated using the new extension loading mechanism.
However, a warn is issued, alerting users and developers that the extension should be updated to use the new mechanism

BREAKING CHANGE: Deprecates `showdown.extensions` property. To migrate, you should use the new method `showdown.extension(<ext name>, <extension>)` to register the extension.

Gruntfile.js

@@ -108,10 +108,11 @@ module.exports = function (grunt) {
 
   require('load-grunt-tasks')(grunt);
 
+  grunt.registerTask('concatenate', ['concat']);
   grunt.registerTask('lint', ['jshint', 'jscs']);
   grunt.registerTask('test', ['lint', 'concat', 'simplemocha']);
   grunt.registerTask('test-without-building', ['simplemocha']);
-  grunt.registerTask('build', ['lint', 'test', 'uglify']);
+  grunt.registerTask('build', ['test', 'uglify']);
   grunt.registerTask('prep-release', ['build', 'changelog']);
 
   // Default task(s).

package.json

@@ -30,7 +30,7 @@
     "url": "https://github.com/showdownjs/showdown.git",
     "web": "https://github.com/showdownjs/showdown"
   },
-  "license": "BSD",
+  "license": "BSD-2-Clause",
   "main": "./dist/showdown.js",
   "scripts": {
     "test": "grunt test"