Implement 'to_vec' and 'from_slice' for no_std

[geigerzaehler]

We implement serde_cbor::to_vec() and serde_cbor::from_slice() in a no_std environment to simplify serialization. For this we use alloc::vec::Vec.

[geigerzaehler]

Unfortunately this does not build with Rust 1.31.0 because the alloc crate is not available. I’d suggest not running the --no-default-features tests on Rust 1.31.0 and documenting that this only works with newer versions of Rust. Alternatively we could introduce an alloc flag (like serde) so that no_std still works with Rust 1.31.0.

[pyfisch]

Is it correct that with this change alloc is always used?
I think there are people using CBOR on systems which do not support allocation.

[geigerzaehler]

Is it correct that with this change alloc is always used?

I think so, though I’m not super familiar with alloc to be honest.

I think there are people using CBOR on systems which do not support allocation.

Ok. It might be best then to put this behind a feature flag. This also aligns with serde and retains compatibility with 1.31.0. I’ll update the PR accordingly.

[pyfisch]

cc @wildarch @chrysn

[wildarch]

I just left one tiny nit in the interest of concise documentation, feel free to leave as is if you disagree.

LGTM! 😄

[pyfisch]

@geigerzaehler By the way this PR broke Travis CI. 😉 See: #154 and https://stackoverflow.com/questions/58249675/travis-ci-fails-to-parse-travis-yml

[geigerzaehler]

Sorry and thanks for fixing. I was wondering where the green checkmark was. To bad Travis does not fail the build when it can’t parse .travis.yaml.