Code styles

[shuaimu]

As we are getting more people working on this, it would be better to have a consistent code style. There are two popular styles: Google and Boost. Although the google style looks a little bit javaish, it is closer to what we have now. So we will use Google style from now on.

Perhaps the most changes that need to be done are:
-- Use two-whitespace indent instead of four (I hate this)
-- Use .cc and .h instead of .cpp and .hpp (I hate this too)

I have a uncrustify config to help the transition here: https://github.com/msmummy/uncrustify-google.