v0.7.0

I've rewritten integer multiplication a second time. The latest implementation is derived from Daniel Schultz's small-prime FFT multiplication implementation in FLINT. It's considerably faster than before, though still a bit slower than GMP's implementation. Malachite now depends on the wide crate for SIMD; once wide 0.8.0 is released, I should be able to improve Malachite's multiplication performance further still. I'm going to hold off making concrete performance claims until then.

Unfortunately, I've discovered that, at least on my machine, Malachite is considerably slower when built using no_std (though still pretty fast!); the main culprit is the libm::fma function, which is considerably slower than the std-only equivalent mul_add. Since I want Malachite to have the best performance possible by default, I've decided to make no_std opt-in. Malachite will build with an std feature by default, and to build it with no_std you will need to disable default features.

Thanks to Will Youmans for implementing some functions around perfect powers, and to all the other contributors to this release.

Next I will focus my attention back on Floats, which have been neglected.