Adds style for tables in readme section

The tables in the READMEs looked a bit off without any styling. I tried to add a style similar to the code block styles, with a #f5f5f5 background and some padding.

I don't know what kind of style you are going for here. Do you think the background looks OK, or should it simply have borders or no background at all?

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### Before
![tablebefore](https://cloud.githubusercontent.com/assets/606374/5377278/81e7763e-8080-11e4-9915-28951d1edb82.png)
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### After
![tableafter](https://cloud.githubusercontent.com/assets/606374/5377280/8b820998-8080-11e4-97d9-bffab276f142.png)