port to rust-ini 0.16

[decathorpe]

• iterating over a loaded ini file sections / properties yields strs now, not Strings, so use to_owned(), not clone() to get an owned value from them
• adapt one test for a small change in an expected error message

[matthiasbeyer]

Where does this merge commit suddenly come from?

[decathorpe]

I needed to resolve merge conflicts because rustfmt was run on the repo.

[matthiasbeyer]

Would you please remove the commit from this branch?
This has nothing to do with the PR and just clutters up the history.

[decathorpe]

You mean I should rebase my original change on the current master instead? Ok, I can do that ...

[decathorpe]

I rebased my changes and bumped to rust-ini 0.16 while I was at it. All INI related tests pass.
I encountered a few test failures that are not related to this change, I did not touch those.

[matthiasbeyer]

Are you still interested in this?

If yes, I created a maintenance fork (read here).
If you want me to, I can include your patches there.

[decathorpe]

Feel free to take my patch, but my interest in the config crate is no longer as big as it was when I submitted this PR.

[matthiasbeyer]

This is merged in config-rs-maint as of master a3f205dc628b59a32de813b3efefbaec4667d217.

[matthiasbeyer]

Hey, would you please rebase this to latest master?