Convenient mixin template for getting your struct working with TinyMap.
Allows to set up a dictionary which is always full.
For each possible key store 0 if it's absent in the dictionary, or 1 otherwise. Bit array is used for compactness.
Use default value specified at construction as an indicator of key absence. That allows to save K.ValueSetSize bits of memory.
Efficient dictionary for cases when the number of possible keys is small and is known at compile-time. The data is held in a static array, no allocations occur.