Is it possible for humans to create a super contagious, super deadly disease...?

Well in order to kill at the rate you describe it would have to be a virus. Also viruses cannot be cured, only treated. Viruses are nothing but DNA and a protein coating so they are difficult to kill. With a virus that no immune system has ever seen (such as a human created synthetic virus) we would be defensless. There would be some random immunities in the human population so it would be nearly impossible to wipe out everyone. A good example of this is bacteria, there is always some bacteria that are resistant to the newest anti-biotics. Such as with Staph, we started treating with methecilin. But some of the Staph were resistant to it. Thus MRSA immerged. (Methecilin Resistant staphylococcus aureus). So we treated with Vancomiacin, but some were resistant. And that created VRSA ( Vancomiacin Resistant staphylococcus aureus). Anyways, sorry for ranting, but it would be very difficult to create a virus that could spread quickly and have a 100% mortality rate.