repeatedly-into as a macro

As long as we are in the extreme, I modified `repeatedly-into` to be a macro (sacrilege, I know) and avoid the small overhead from the fn calls/creation. 

benchmark is against master this time (the code is against dev):

`macro`
{:fast {:thaw 3534}}
{:fast {:thaw 3472}}
{:fast {:thaw 3428}}
{:fast {:thaw 3408}}
{:fast {:thaw 3431}}
{:fast {:thaw 3416}}

`fn`
{:fast {:thaw 4148}}
{:fast {:thaw 4048}}
{:fast {:thaw 4039}}
{:fast {:thaw 4063}}
{:fast {:thaw 4059}}
{:fast {:thaw 4054}}

I would normaly not even try to apply such optimisations (it's a bit ugly to read/use) but it's here if you want it.