uniform_01 generator

[DiscreteLogarithm]

There's this comment in uniform_01.hpp:

Note: The current implementation is buggy, because it may not fill
all of the mantissa with random bits. I'm unsure how to fill a
(to-be-invented) @c boost::bigfloat class with random bits efficiently.

We do have an efficient algorithm (see section 4 of this preprint) and a C++ implementation capable of generating all representable floating-point numbers in [0,1). It fills the mantissa with a random integer and generates a geometric random number for the exponent. In the double precision case, it is even faster than simply multiplying a 64-bit integer by 2^-64 and in the single precision case it's only 25% slower than multiplying a 32-bit integer by 2^-32 (when used with the MT19937 URBG).

If you are interested we can help to integrate it into boost.