index: signature separate export
index: assembly separate export
signature/lib: if there's no opts assign expires

the older method was crashing, because if the optional `opts` parameter
was missing then there was an exception being thrown.

So expires is defined outside the check, the check is in place for `!=
null` and now everything is working even with missing `opts` parameter.
gitignore: created
test-signature: created
assembly/test: created