Fix #41: spacing in string templates

Issue #41 was really two issues:

1. Discussion how string templates should be spaced; it was decided that
   they should be spaced like range operators (#35, 4c761b7)
2. Bug where spacing information was lost for multi-line tokens

Both are fixed in this commit.

Also, another bug surfaced where closeContext0 couldn’t handle the case
that the token whose context was closed wasn’t in the token queue any
more; fixed as well.