Clean up precomputed logs tables

* remove duplicate identical 2k table from fast_log.rs (removed file)
* move two tables into dedicated files, one table per file (they are big, hard to work with them ohterwise)
* renamed them to follow Rust naming conventions - they do not seem to be publically exposed, so should be safe from versioning perspective.
* changed the type of the `logs_8` to be `[floatX; 256]`, same as `log_16`.  This eliminate casting everywhere.

Author: nyurik