Some minor improvements to our array replacement:

* the array synopsis in the standard uses struct, so why don't we?
* add method empty (demanded by the standard, many more are actually missing)
* consistently use std::size_t instead of size_t (for std::array it should even be std::size_t)
* simplify operator<<
* unify indentation (to 2)
* make_array is a function and not a method
* improve comments on the preprocessor branches (to improve readability)

[[Imported from SVN: r6868]]