prevent panic on parser io error

[kpwebb]

The library panics on files that don't contain valid text. I added an error check ahead of the unwrap on line, and a new Parser IO Error type.

[gwbres]

Hello @kpwebb,

thank you for the suggestion 👍

I think I wrote this unwrap for the simple reason I don't understand what might go wrong here.
Is that an I/O (reading) issue, or invalid UTF-8 that could not be interpreted ?
Either way, I'm fine with catching the error.

But if this happens in the header, the parsing will most likely fail completely.

[kpwebb]

Yeah the error I'm seeing: when an invalid file is opened the lib panics due to UTF-8 encoding issues. I'm fine with a more generic error being used as a catchall as a panic causes a lot of problems for downstream users.

[gwbres]

I/O error is already caught & wrapped, we can simply replace the unwrap with ? that would return an Error at this point.
The debug/panic trace is then the std::io trace

[gwbres]

If you don't mind, I want to merge my pending PR and close a few issues before publishing a new release.
This will probably take 1 or 2 days