Merge branch 'am/pathspec-from-file'

Merge branch 'am/pathspec-from-file'

A few commands learned to take the pathspec from the
standard input or a named file, instead of taking it as the command
line arguments.

* am/pathspec-from-file:
  commit: support the --pathspec-from-file option
  doc: commit: synchronize <pathspec> description
  reset: support the `--pathspec-from-file` option
  doc: reset: synchronize <pathspec> description
  pathspec: add new function to parse file
  parse-options.h: add new options `--pathspec-from-file`, `--pathspec-file-nul`