Add support for `cascade_strategy` config option to change the way we iterate
through the subs.
Merge pull request #438 from mattcottingham/dev

Fix libc6 dependency in CMakeLists.txt
Use a const iota-based enum to store the cascade strategy instead of checking
against a string value every time.
Typo.
Merge pull request #437 from mozilla-services/features/multidecoder-cascade-strategy

Add support for `cascade_strategy` config option