The changes are mostly mechanical

- replace use of the blobcode vmod with vmod blob and adjust to new
  function signatures
- use struct vrt_blob for blobs and adjust to new struct members
- use separate pointers for generating output (blobs are const)
- use optional arguments for functions (minimal adjustments of
  existing code)
- replace WS_Reserve() with WS_ReserveAll()
- wipe needs the TRUST_ME() macro to un-const blobs

unresolved issues:

- padding errors lead to "vmod blob error: cannot encode, out of space",
  the respective tests have been moved to
  tests.disabled/padding_error.vtc