Hack pipeline

Rough draft of the real-time pipelines.
no, these are all just constant filling.  the first two are forward, the second two are backwards

 - forward [ 1, na, 2, na, na, 3] -> [1, 1, 2, 2, 2, 3]
 - backward '' '' -> [1, 2, 2, 3, 3, 3]

There is interpolation (even ones that are time-index aware), but we just need to add another bit to the column spec to be able to turn that on.