Forward the parsing error while parsing a module to the parent module

[ogoffart]

Otherwise we just unwrap it and the error message is not good enough

[ogoffart]

I did not test enough what happens when there is an error in another module than the root module. I quickly noticed while developing on another crate that the error is not good enough.

(Would be great to have compilation error tests)

@mystor I guess this would qualify for a 0.15.1

[ogoffart]

I took the freedom to merge the pull request as it is quite simple.

I also made another small change.

I think this qualify for 0.15.1 as it improve error reporting.

[mystor]

published as 0.15.1

[ogoffart]

Thank you!