feature added - attribute-support for every merged svg object

+ added code in the task - mostly string concatenation of attributes, defined in options
+ added a test task in Gruntfile.js
+ added a test and an appropriate file to compare

message to @FWeinb: it started with a weird bug caused by writing viewBox the right way (v0.2.3). In v0.2.2 the svgs didnt scale - accidently and caused by writing 'viewbox' the lower-case-way. But for me, this behavior was the one I needed to (open/close animations).
After some research I found the reason [here](http://www.justinmccandless.com/blog/Making+Sense+of+SVG+viewBox%27s+Madness) and [here](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/preserveAspectRatio). So I decided to solve my issue in a more generally way. maybe you wanna merge it into the original package.
Suggesting this function to generate the attribute string.
```js
var genAttrStr = function ( attrs ) {
  var result = '';
  Object.keys(attrs).forEach(function (key) {
      result += ' ' + key + '="' + attrs[key] + '"';
  });
  return result;
}
```