Merge branch 'lsfd-pidfd' of https://github.com/masatake/util-linux

Merge branch 'lsfd-pidfd' of https://github.com/masatake/util-linux

* 'lsfd-pidfd' of https://github.com/masatake/util-linux:
  lsfd.1.adoc: write about how pidfds are represented in NAME column
  lsfd: show pids targeted by pidfds in NAME column
  lsfd: add a helper function to get 'struct proc' object for given pid
  lsfd: introduce a method table for supporting various anon inodes
  lsfd.1.adoc: write more about TYPE column
  lsfd.1.adoc: fix a wrong formatting
  lsfd.1.adoc: fix typos
  lsfd.1.adoc: use monospace face instead of italic face
  lsfd: delete __unused__ attr from a used parameter