Refactor code for an easier build process

I refactor code to put "main" package on root.

Any "dvara" package is in "lib" folder.

This organisation let us using gobuild.io

Here is an example for this project: http://gobuild.io/download/github.com/guilhem/dvara
It's exactly the same code minus a change to import the good "lib".

I'm not a go expert, but it seems to be quite simple and powerful :)
Criticizes are welcome!