New feature: copy the content of a screen region

This pull request includes: 
<ul>
<li>A new method (copyRegion) to copy the content of a screen region.</li>
<li>An example on how to use copyRegion method</li>
<li>New methods to get the four corners of a screen region</li>
<li>A new method to create a custom screen region on a given screen/monitor</li>
</ul>