0.9.0

Yay new version already! A pretty significant API change, too! ��

Breaking Changes

SourceSpans have changed a bit: for one, they're based on offset/length now,
instead of start/end. For two, they have a new Option<String> field,
label, which is meant to be used by reporters in different contexts. For
example, highlight snippets will use them as the labels for underlined
sections of code, while the snippet context will use the label as the "file
name" for the Source they point to.

• protocol: new SourceSpans with labels (acfeb9c5)

Bug Fixes

• derive: allow unused variables for the snippets method (f704d6a9)

Features

• protocol: implement From<(usize, usize)> for SourceSpan (36b86df9)