Insert a new Skiplist implementation, repair links and add self-hosted images

[MauriceGit]

Hello Sean,

as discussed per mail, here is my pull-request.

What has changed:

• Included my own Skiplist implementation (including description).
• Added two more functions that are close real-world cases (random Inserts, random Deletes) that nicely show the logarithmic behaviour of insertion/deletion across all benchmarks.
• Attached the actual output.csv, openOffice table and generated graphs in the graphs folder.
• All graphs in the README are now self-hosted in the repository, removing the dependence to imgur.
• Recreated all graphs so they accurately show the current benchmarks.
• Repaired the links in the readme.

What you have to do:
Nothing really. If you like the format and new graphs (have a look at my fork:https://github.com/MauriceGit/skiplist-survey), just accept the pull-request and you're done.

Otherwise re-run the benchmark and re-create the images from your data.

Right now, my implementation is not concurrent so I didn't take the time to create concurrent benchmarks. If I change that, I will create the corresponding benchmarks and make a new pull-request.

Best regards and thanks!
Maurice