Stabilize clamp
Tracking issue: https://github.com/rust-lang/rust/issues/44095
Clamp has been merged and unstable for about a year and a half now. How do we feel about stabilizing this?
make exp_m1 and ln_1p examples more representative of use
With this PR, the examples for `exp_m1` would fail if `x.exp() - 1.0` is used instead of `x.exp_m1()`, and the examples for `ln_1p` would fail if `(x + 1.0).ln()` is used instead of `x.ln_1p()`.