fix no-std for optional math libraries

[Firestar99]

Currently the optional math library dependencies enable the default-features for those libraries, causing eg. glam to enable the std feature, breaking no-std environments like rust-gpu. This PR disables the by default allowing the end user to enable what they need.

I'm unsure but this may break dependent projects if those do not explicitly declare a dependency on the math library, but only use it via this crate. For example glam will get the std feature disabled, but it requires that either std or libm feature is enabled, otherwise it won't compile. But I'd expect that specific case to basically be non-existent and an easy fix: just declare the math library explicitly.

[LPGhatguy]

This seems like a reasonable fix to me! I'd be very surprised if anyone depended on Crevice but then did not have the math libraries in their tree configured how they'd like them.

It looks like there might be some CI failures that we probably need to sort out.

[Firestar99]

with the latest commit failed CI runs just fine locally

[LPGhatguy]

Thanks for the fix!