Cleaning up and preparing for layers

Running dialyzer shows a lot of todo's
Removed 12 dialyzer errors by editing one line #winning
Let's postpone declaring behaviour until all dialyzer errors are fixed.
Dialyzer part ][
Added something similar to a maybe monad; time for some proper cleaning!
Uniform errors first
Aha, a proper maybe! We're en route!!
Well, dialyzer exposed a lot of weaknesses!

I am starting to become a fan of it!
Only 3 dialyzer errors left in fdb.erl
Removed the last few potential bugs in `fdb.erl` caused by missing types

Thank you dialyzer!
Some more cleaning... Needed to refactor the nif interface
Got rid of ALL the dialyzer errors
Range doesn't work yet for subspaces; don't see it ATM

Tomorrow should bring some inspiration