Refactor parser for more efficient code utilisation

This is a large refactor that makes the code flow much simpler. The parser still needs better debugging infrastructure.

* Unimplemented variables are no longer used
* Tags are now handled
* bstr wrappers are now handled implicitly where necessary
* Added a new k/v pair handler that processes a key with a type in one shot.
* Added distinct handling for arrays (a sequence of identical types) and lists (a sequence of different types)
* Integrated COSE signature handling
* Added a const array initializer helper macro so that parser element counts are calculated at compile-time.
* Added an image verification handler that consumes SUIT_Digests and handles the algorithm correctly
* Verify manifest against authenticated hash before processing