Ignore Cargo.lock (this is a library).
Add now-necessary lifetime bounds.
Switch to official Travis Rust support.
Shift an impl into the appropriate module.

This has now become necessary.
Switch to the now-public std::any::AnyPrivate.
Fix warnings.

With the exception of the HeaderShowAdapter dead_code warning (solved by
making it public), they were all deprecation warnings.
Fix Header.fmt_header for Header trait objects.

I guess deref behaviour around boxed trait objects changed, because that
code used to call the method on the wrapped object but had begun to be a
recursive call instead. Scary stuff, with no compile error…