mega-buffering passthrough block

[guruofquality]

Create a simple passthrough block with a "boundless" input buffer. The purpose is to be able to buffer vast amounts of data in memory when it cannot be read out fast enough -- at the expense of 1) backing up the flow and 2) consuming available PC memory resources.

This block will have custom input buffer manager that will 1) allocate more buffers on demand, and 2) never report empty (or report empty at some specified maximum).