Improve result querying

[serradura]

Added

• Add the BCDD::Success and BCDD::Failure modules. They are key to checking whether a result is a success or a failure independently of whether it is a BCDD::Result or a BCDD::Context.
• Add BCDD::Result#type? to check if the given type is the result type.
• Add BCDD::Result#is? as an alias for BCDD::Result#type?.
• Add BCDD::Result#method_missing to allow the type checking through method calls. For example, result.ok? will check if the result type is :ok.

Note: All the methods above are available for the BCDD::Context as well.

Changed

• (BREAKING) Change BCDD::Result#deconstruct_keys to return a hash with the keys :type and :value when one of these keys is present. Otherwise, it will return the value itself.