Panics have changed with Errors for NewWriter And NewReader

[olimpias]

Errs are handled more gracefully.
Unit tests are added for NewWriter and NewReader.

Ref Task: #241

[achille-roussel]

First, thanks for the contribution and raising the issue!

I don't think we can make this change as proposed tho, because we would be breaking pretty much all programs using this package.

What do you think about taking a different approach, and introducing a mechanism for validating the configuration values that are passed to reader/writer, for example:

func (c *ReaderConfig) Validate() error {
    ...
}

Then the program can explicitly call Validate to detect malformed configuration before it creates the reader, and we can leave the signature of NewReader/NewWriter unchanged.

What do you think?

[olimpias]

Sure, it makes sense for backward compatibility. I will do the required updates.

[achille-roussel]

Looks great, thanks for the contribution!