Using same instance for tests so they fail less because of Simplenote se...

Hi Daniel,

I have been using your simplenote.py library for some time now for my sublime text 2 plugin, it has been working great so far, so thanks for your work :)

Now I wanted to adapt my plugin for sublime text 3, which uses python 3 as language instead of python 2, so I forked your project and started adapting it to work on python 3. First thing I had to do was re-work a little the tests since Simplenote seems to be rejecting the strategy of logging for each request that they were using before. I added also a delay between the operations so Simplenote doesn't reject the requests. Hope this is alright. I will soon send a pull request for the python 3 version (which is based on this commit).

![after delay](https://cloud.githubusercontent.com/assets/492246/5551189/2e3f7638-8b9f-11e4-9b1a-879b4e6999b0.png)
![before delay](https://cloud.githubusercontent.com/assets/492246/5551190/2e49487a-8b9f-11e4-89f8-0b0f921f3534.png)

Regards and happy holidays.