CommonJS approach
Delete php build script and crafty-local.js
Grunt watch task for continues building the crafty.js file.
Provide source-map support for a development version of Crafty.js
Update `getVersion` method

Using `require` is possible to dinamically get library version from
package.json `version` property.
Merge pull request #568 from kevinsimper/commonjs

Browserify Crafty.js
Merge pull request #571 from potomak/feature/fix-version-method

Feature/fix version method