Add support to use 100% of container

[LeoNero]

Based on #20 , it is a good idea to implement the option to use 100% of the container. The suggested usage is as follows:

<Zoom
  img=""
  zoomScale={3}
  height={600}
  width="100%" // use 100% of the container
  transitionTime = {0.5}
 />

"width" would receive either a string (which would contain how much % the user would like to set the width), or a number, which would be the size of the width in pixels.

[singhaishwarya]

any update?