Bugfix: type() doesn't support unicode, cast to str.

Signed-off-by: Martin Raspaud <martin.raspaud@smhi.se>
style: use in instead for has_key()

Signed-off-by: Martin Raspaud <martin.raspaud@smhi.se>
Allow reading several files at once in eps_l1b

Signed-off-by: Martin Raspaud <martin.raspaud@smhi.se>
Allow reading several files at once in viirs_compact.

Signed-off-by: Martin Raspaud <martin.raspaud@smhi.se>