Decide on code style

[MatthijsBurgh]

@meyerj Ok.

So are you giving me a card blance to go ahead and fix the styling of the entire repo? Which will affect the git blame a lot.

True. I leave that to @smits.

But as a first step we would have to decide on a code style to apply for this project. Using 4 spaces for indentation and spaces inside parenthesis was quite common for older Orocos code. Other influences are the ROS C++ style guide or ROS 2 C++ code style, which is derived from, but not compatible to Google C++ style. Without having made that decision first, it does not make much sense to apply style-changes in a few places only based on personal preference, and consistency with existing code is more important.

Originally posted by @meyerj in https://github.com/orocos/orocos_kinematics_dynamics/pull/256#issuecomment-640224740