0.3.0

• Introduced advanced header matchers: Matcher::Any to match only by the field name and Matcher::Missing to match the absence of a particular header. These are used within the Mock::match_header call.
• The old behaviour of matching the header value by &str was kept backwards compatible.

0.2.5

• Explicitly set an empty body for non-matching routes (prevents hanging requests for non-matching routes).
• Added more tests.