0.9.2 : Better error reporting

Maintenance release introducing the following changes:

Features & improvements

• add more details regarding failing requests in case of network errors.
• improve error reporting formatting and cosmetics across the board.
• avoid unecessary placeholders resolution if possible.
• GenericAssertion abstract the diffability through a typeclass (all common instances provided).
• introduce addToWithHeaders to add headers to the with-headers collection.

Breaking changes

• the HttpService session keys variables are now lower-cased
• AssertStep and GenericAssertion have been moved a package deeper to com.github.agourlay.cornichon.steps.regular.assertStep