iota API was chaged

Before v0.9.0:

auto a = iota(3); // 0, 1, 2 typeof sizediff_t
auto b = iota([3], 2); // 2, 3, 4 typeof int

Since v0.9.0:

auto a = iota(3); // 0, 1, 2 typeof sizediff_t
auto b = iota([3], 2); // 2, 3, 4 typeof sizediff_t
auto c = iota!int([3], 2); // 2, 3, 4 typeof int