Lexicographic Keys
References
1 Matula and Kornerup 1983 - An order-preserving finite binary encoding of the rationals
http://www.acsel-lab.com/arithmetic/arith6/papers/ARITH6_Matula_Kornerup.pdf
2 Kornerup and Matula 1995 - LCF: A Lexicographic Binary Representation of the Rationals
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.108.5117&rep=rep1&type=pdf
3 Z85 spec
https://rfc.zeromq.org/spec/32/