Flow should not need capnp (ipc* does); ~Same changes made to flow/same-stuff also applied here (details omitted); highlight: manual workflow runnability; highlight: create tarball with docs and landing page which also hugely speeds up the artifact generation. Minor tweak for consistency in `make` arg order. Added TODO regarding how our CMake script should be able to determine jemalloc-prefix by itself, though giving it manually is certainly supported too. Renamed pipeline a bit (it is Flow-IPC; might as well keep "branding" consistent. #17