Add pelican-flickr plugin.

I have created a pelican plugin to add [Flickr] photosets & photos in a Pelican web site.

It uses a local cache to speed up processing time, and depends on [flickrapi]

I have already created a Pyhon package pelican-flickr. You can view a demo rendering on [my website]

Can you please consider merging it in pelican-plugins ?

Thanks for your time.

[Flickr]: http://flickr.com
[flickrapi]: https://pypi.python.org/pypi/flickrapi
[pelican-flickr]: https://pypi.python.org/pypi/pelican-flickr/0.1.1
[my website]: http://bastien.abadie.me