Consider removing old API syntax from documentation

[sv3ndk]

I am a newcomer to this project, I find it very useful, thanks for working on it.

When reading the documentation, I was puzzled at first to first read code snippets based on the ForEachTestContainer and ForAllTestContainer syntax, then to discover a new API based on TestContainerForAll and TestContainerForEach was now the recommended approach.

I understand the new API syntax has been around for about 3 years now, so I suggest to re-write all code snippets with it as well as Container.Def (most of which is already present in the "new API" section of the doc), and to either remove the mentions of the old syntax or to move it down to some "legacy" section or so.

This seems easy enough to do, so if you agree I'm happy to submit a minor PR with such change.

[dimafeng]

@sv3ndk Agree! Any help would be appreciated!

[sv3ndk]

Great! I'll make time for that this week-end