- Using Q.mul_2exp for pow2
- Simpler and correct implementation for log2
- Declaring the ten constant only once

- Add a Rational module that implements a field over rationals.
- Add rationals to Datatype
- Move field, nat, finite and linear into libraries/arithmetic
- Update linear_filter_test to use the Rational module
- Update oracles

- Type.register returns the first registered type instead of a new one

(Messages emitted via Log.printf are never truncated.)

Rich_text: do not silently truncate buffers, but export function [truncate].
Log: uses [Rich_text.truncate] on messages printed on terminal, and prefix
     truncated messages to indicate the truncation.

Add a record with 2 fields : tnode and tattr

The new parameter is -eva-cache-size.