Rust pop-quiz answer: accurate pricing of actively-traded tokens on Kujira FIN

#Rust pop-quiz answer to rewriting token-price-calculation.

A complete rewrite has now 60+ tokens accurately priced from active trades in @TeamKujira FIN.

https://github.com/logicalgraphs/crypto-n-rust/blob/main/src/libs/crypto/types/books.rs#L147-L237

This solution uses HashMap chaining and higher-order fuctional composition to avoid unnecessary collection-mutation. 

The above is part I to get to the solution.

Next comes part II: accurate order book volumes.