Dump all the errors from different files

[alyoanton9]

Clarification and motivation

As we have right in-place annotations now (<!-- xrefcheck: ignore <mode>-->), there can be broken markdowns.
For example:

1. <!-- xrefcheck: ignore file--> located in the "middle" of the file (not right after the comments at the top) causes Error when scanning .\markdowns\with-annotations\no_paragraph.md: expected a PARAGRAPH after "ignore paragraph", but found HEADING (9:1-17).
2. A typo like <!-- xrefcheck: ignore ile --> causes Error when scanning .\markdowns\with-annotations\unexpected_ignore_file.md: unrecognised option " "ignore ile" perhaps you meant <"ignore link"|"ignore paragraph"|"ignore file"> ( 9:1 - 8:0)
   And so on.

Currently, xrefcheck fails immediately after the first observed error because die is used right in markdownScanner:

markdownScanner path = do
    errOrInfo <- parseFileInfo . decodeUtf8 <$> BSL.readFile path
    case errOrInfo of
        Left errTxt -> do
            die $ "Error when scanning " <> path <> ": " <> T.unpack errTxt
        Right fileInfo -> return fileInfo

And propagated on a higher level, to Main.
What we want is dumping all the errors from different markdowns and then print them as a final xrefcheck's result together with the broken links.
A possible solution is to add a custom exception type for scanner errors, this way exceptions can be reasonably caught outside if necessary (not in inner components).

Acceptance criteria

1. No die in inner components.
2. All the errors are printed as a result together with the broken links.

[dcastro]

@Sereja313: Andrii had previously started working on this issue. He had a Draft PR (see #87). I'm not sure how close to completion it was - can you please have a look at the PR?

Let me know what you think of the PR, and whether you think it's best to just continue working on that branch (it's been a while, rebasing that branch might lead to lots of merge conflicts) or to start from scratch with your own approach.

[Sereja313]

@dcastro, It looks like not much has been done, so I started from scratch to avoid merge conflicts.

[dcastro]

@Sereja313 Sounds good! 👍