fdo#36313: allow passing FilterOptions via cli

Examples:
  --infilter="Text (encoded):UTF8,LF,,,"
  --convert-to "html:XHTML Writer File:UTF8"
  --convert-to "txt:Text (encoded):UTF8"

Change-Id: I69a0524ef63f6d486637d68280331528d1001b56
(cherry picked from commit 45ba4d79d968f81f74ef0c4588fd15b1ce91153f)
Signed-off-by: Stephan Bergmann <sbergman@redhat.com>