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First working version. The plugin has no settings (headless)
Usage:

[wplink id="{css class}" url="{destination-url}"]

The plugin appends "amz" to the id class.

Example:

[wplink id="us" url="http://www.amazon.com/dp/095642760X"]

output:

<span class="amz-us"><a href="http://www.amazon.com/dp/095642760X"
class="amz-us">Buy Now</a></span>

Styling will usually hide the "buy now" text, although next iteration
should probably allow users to choose which text they would like to
display, e.g. text="" attribute.

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