Extra items in #[schemars(...)] attributes are silently ignored

[GREsau]

This currently compiles:

#[derive(JsonSchema)]
#[schemars(wasd, qwerty = "uiop")]
pub struct MyStruct;

It should cause a compile error to prevent people from mistyping or trying to use unsupported attributes

[GREsau]

A fix for this was committed in 780c728, but is commented out as it will be a breaking change. I'll uncomment it (which will actually apply the fix) when releasing v0.8 - done in b0a2f99