trident validate should check LF-line endings

[stschiff]

We recently came across an issue where I accidentally committed a Janno-file that had Windows line endings (CRLF) (see poseidon-framework/community-archive#214). Checksums were computed based on these files and committed, and the package validated. We only caught this because git converted the line endings implicitly into LF, which in turn changed the file and invalidated the checksum.

Whether or not we divide to change git-attributes (see poseidon-framework/community-archive#215), we should build in a check within trident validate that checks for line endings in all text-files that are checksum-validated, including .ind, .fam, .snp, .bim, .vcf (in the future), .geno, .bib, .janno.

[nevrome]

This is probably the same issue as #302.

In today's discussion we concluded that such a check is not necessary in trident, but instead only in the public archives. Maybe that's what we try for now. Requiring one specific line ending is a change we should first encode in the Poseidon schema.

[stschiff]

OK, we could still discuss a warning. I think even without mentioning this in the schema, we can make it "recommended" to use LF.