Allow bool for readme in manifest

[heaths]

Fixes #234

[ehuss]

I'm a bit confused about this change. Cargo doesn't expose the true/false status as a boolean via metadata. It should only ever be a string or null. Can you say more about what exact scenario this is trying to address?

[heaths]

A manifest can explicitly declare it has no readme, as may be the case when using wasm-pack, for example. See rustwasm/wasm-pack#1215 for details, but effectively readme = false is allowed per documentation, which is intended to disable readme resolution. For example, even if you had a README.md but didn't want it to show in your crate description, you could set readme = false. Since wasm-pack took a dependency on this crate, I wanted to fix it upstream so that we could detect if the readme was explicitly elided.

[ehuss]

Sorry, maybe I wasn't clear. The true/false value of the readme field isn't exposed by cargo (see cargo metadata). This crate is just representing the values that cargo itself exposes via the cargo metadata command. A value of readme=false is translated to null, and a value of true is translated to "README.md".

[heaths]

Ah. Thanks for clarifying. I looked through the project de/serialization a bit but didn't realize you were effectively parsing the output of a command. Given the "translation" you mentioned, that should still be enough to go on to determine if the readme resolution was disabled, though.

Thank you.

[jplatte]

Well, if the cargo metadata output indeed makes a difference here (null vs. an absent field, or is it never absent?), I think it would be reasonable for this crate to reflect that. I wrote the js_option crate for exactly this use case of distinguishing null vs. missing, though it might not be desireable to take on the extra public dependency here.

[ehuss]

cargo metadata does not distinguish a difference (the field is always present).