Move to a cache using hashes as keys

[samuelchassot]

The size of one key is the following: CacheKey size = 32 bytes and serialised size = 322 bytes

[samuelchassot]

An example of the cache size reduction on bolts/fp-principles/huffman-coding:

• binary format: 5'572'205 bytes (~ 5.6MB)
• hash format: 15'680 (~16KB)

So a reduction of 355x.