Support for files with (or without) diffing

[bjchambers]

It would be helpful if insta could also be used for managing file contents. For instance, some tests may produce CSV (and the plain text / diffing based on strings i great), but if other tests want to produce Parquet files (a binary format) they can't use insta.

How difficult would it be to have something like insta::assert_binary_file(<path>) and insta::assert_text_file(<path>)?

[mitsuhiko]

What would the behavior of this be when the mismatch happens?

[bjchambers]

It could be similar to https://docs.rs/goldenfile/1.1.0/goldenfile/ - output the diff (or diff hashes if the files are binary) and allow accepting to overwrite the expected file (or hash).

[mitsuhiko]

I would be accepting a patch for it but I assume the work required would be quite significant since everything in the system currently assumes unicode strings.

[mitsuhiko]

Closing this as duplicate of #196