Update approx to 0.5 with some small fixes

[ghost]

No description provided.

[yoanlcq]

Hi, I'm curious about what made you add #![recursion_limit = "256"].
Apart from that I see no problem with merging this.

[ghost]

Rust 1.59 if i remember correctly was complaining about not been able to compile a test on my computer. here a copy of the error.

error: recursion limit reached while expanding reduce_fn!
--> src/vec.rs:47:69
|
47 | ($fn:expr, $a:expr, $b:expr, $($v:expr),+) => { reduce_fn!($fn, reduce_fn!($fn, $a, $b), $($v),+) };
| ^^^^^^^^^^^^^^^^^^^^^^^
...
3340 | vec_impl_all_vecs!{c #[repr(C)] c #[repr(C)] repr_c}
| ---------------------------------------------------- in this macro invocation
|
= help: consider increasing the recursion limit by adding a #![recursion_limit = "256"] attribute to your crate (vek)
= note: this error originates in the macro reduce_fn (in Nightly builds, run with -Z macro-backtrace for more info)

[yoanlcq]

Published in 0.15.7