Evaluate Microsoft's FASTER key-value store as a potential replacement of RocksDB

[zah]

Microsoft has recently published a new open-source embeddable key-value store that reports substantial performance improvements over RocksDB on certain workloads:

https://github.com/Microsoft/FASTER https://www.microsoft.com/en-us/research/uploads/prod/2018/03/faster-sigmod18.pdf

Prior to shipping the server-side version of Nimbus intended for full nodes, we may evaluate FASTER against the current alternatives (RocksDB and SQLite at the moment).

For server-side full nodes, the primary selection criteria would be the database throughput, while on the primary target of Nimbus (mobile devices) it makes more sense to optimize for battery drain, memory and space usage and binary size.