options("RestRserve.headers.split"). See #187, #189. Thanks @DavZim.
.resplaceholders as handler argument names allows to leverage autocomplete
multipart/form-dataparsing, see #160 for details
stdinfile descriptor is closed inside child processes
stdinmore reliably (but still there is race condition because multiple child processes write to the same stdout)
jsonlite::fromJSONfor safety reasons