Support CSS3 transition

**I'm submitting a feature request**

* **Library Version:**
1.0.4

**Please tell us about your environment:**
* **Operating System:**
Windows [7|10]

* **Node Version:**
10.1.0

* **NPM Version:**
6.4.0

* **JSPM OR Webpack AND Version**
webpack 4.0

* **Browser:**
all

* **Language:**
TypeScript 3.0

**Current behavior:**

`animator-css` can not work with css3 `transitions`. you can find the detail [here](https://discourse.aurelia.io/t/how-to-use-css-transitions-in-aurelia-animator-css/1827)

**Expected/desired behavior:**

* **What is the expected behavior?**
It would be great if we have `transitions` as option beside `animations`.

* **What is the motivation / use case for changing the behavior?**

@zewa666
I think it is so tricky I am not sure works for every scenario but as you asked me you can find the following sample.

**Detecting transition start**
[Website](https://www.madebymike.com.au/writing/detecting-transition-start/)
[Implementation](https://codepen.io/MadeByMike/pen/sBjzn)

Start by reading the existing animator-css implementation and the linked Aurelia discussion about CSS transitions. Review the linked transition-start article and CodePen for the proposed detection approach, then define how a transitions option should behave alongside animations. Done means CSS3 transitions are supported without breaking existing animation behavior.

Written by the indexing model from the issue text.