Add a GitHub actions workflow which runs `cargo build --all-features`

[mjhouse]

Add a GitHub actions workflow which runs cargo build --all-features (#39)

[vcrn]

I guess our options are:

• Add this step to the already existing workflow rustdoc.yaml (and rename it I guess).
• Create a new separate workflow file. Which one do you prefer @mjhouse?

[mjhouse]

@vcrn We can add it to the existing workflow.