Add checkstyle to enforce consistent source formatting.

[tomwhite]

I think it would be good to use checkstyle on the source code, so that it's in line with the style used by the Hadoop project. This PR is a demonstration of what that would look like. It's a bit disruptive, but it shouldn't be needed again. if you're amenable to this @damiencarol, then I can do the same for the whole source tree.

[damiencarol]

@tomwhite Very mean PR. I'm ok with that.

[tomwhite]

Fixed the travis error. Thanks @damiencarol.

[damiencarol]

@tomwhite I'm merging this one. I will continue to add more files to checkstyle conf.

[tomwhite]

Great - thanks @damiencarol!