Reads zettel data from a file (or from standard input / stdin) and renders it to standard output / stdout.
This allows Zettelstore to render files manually.
```
zettelstore file [-t FORMAT] [file-1 [file-2]]
```

; ''-t FORMAT''
: Specifies the output format.
  Supported values are:
  [[''html''|00001012920510]] (default),
  [[''md''|00001012920513]],
  [[''shtml''|00001012920525]],
  [[''sz''|00001012920516]],
  [[''text''|00001012920519]],
  and [[''zmk''|00001012920522]].
; ''file-1''
: Specifies the file name, where at least metadata is read.
  If ''file-2'' is not given, the zettel content is also read from here.
; ''file-2''
: File name where the zettel content is stored.

If neither ''file-1'' nor ''file-2'' are given, metadata and zettel content are read from standard input / stdin.