Merge branch 'feature/simplify-foreach' into 'master'

Short circuit Hybrid::forEach for integer_sequence

This reduced the template instanciation depth drastically.
E.g., for range=`integer_sequence<21>` is changed from 319 to 84.

This is especially important for clang, because this has a default max-depth of 256 in contrast to gcc (900).

See merge request !162