`std.meta.Stride` was added

$(REF Stride, std,meta) allows selecting a subset of template by a step size and offset:

---
alias attribs = AliasSeq!(short, int, long, ushort, uint, ulong);
static assert(is(Stride!(3, attribs) == AliasSeq!(short, ushort)));
static assert(is(Stride!(3, attribs[1 .. $]) == AliasSeq!(int, uint)));
---
