Align and minimize One

[bernhardmgruber]

Fixes #267.

[j-stephan]

We probably want some curly braces behind the if. I think some compilers even warn about this. Also in the other instances if you change this.

[bernhardmgruber]

That's a stylistic question, which I strongly oppose. I know the argument that adding braces could avoid accidentially misindenting a statement, believing it belongs to the if statement. However, clang actually detects such misalignment. Furthermore, our code base is clang-formatted so we would immediately notice. So the only thing braces add here is an extra LOC, spreading the code a little vertically. And I prefer to the code to be compact. I also know clang-tidy can add these braces automatically, so at some point we will have the vote and then we can see what happens :)

[j-stephan]

Is One<ArrayDims, RecordDim, false, FlattenRecordDimMinimizePadding> missing on purpose?

[bernhardmgruber]

That is a valid mapping, but I do not see the use case. One<..., true, ...> adds padding to respect alignment, so adding field permutations make sense, to play with this padding.
One<..., false, ...> does not add padding, so permuting the fields has a far smaller effect. So I want to advertise it less.