v3.6.0

• callr now supports starting an R process with a different architecture,
  so on Windows 64-bit R can start a 32-bit R background process, and
  vice-versa (#95).

• callr now handles symbolic arguments properly, and does not evaluate them.
  E.g. callr::r(function(x) x, list(quote(foobar))) works now (#175).

• callr::r_session does not leak file descriptors now in the sub-process
  (#184).