Correctly render tab stops in --show-all

[Synthetica9]

New behaviour:

───────┬────────────────────────────────────────────────────────────
       │ STDIN
───────┼────────────────────────────────────────────────────────────
   1   │ ··├┤␊
   2   │ ·├─┤␊
   3   │ ├──┤␊
   4   │ 12345678␊
───────┴────────────────────────────────────────────────────────────

Old behaviour

───────┬────────────────────────────────────────────────────────────
       │ STDIN
───────┼────────────────────────────────────────────────────────────
   1   │ ··├──┤␊
   2   │ ·├──┤␊
   3   │ ├──┤␊
   4   │ 12345678␊
───────┴────────────────────────────────────────────────────────────

Does not work with multi-width characters, yet, is this a requirement? If so, how should this work with unicode escaped characters?

[Enselic]

Nice 👍 I skimmed the code and it looks reasonable. Before a detailed review, can you please add at least one test (preferably more as long as it makes sense, e.g. with different tab sizes) for this in https://github.com/sharkdp/bat/blob/master/tests/integration_tests.rs? I.e. invoke the binary and assert on stdout.

That way we can be sure that this contribution and use case will never stop working.

[Synthetica9]

Okay, added two integration tests. Not sure about the names, feel free to suggest better ones.

[sharkdp]

Very nice! I like it.

Could you please add an entry to the CHANGELOG? See instructions here: https://github.com/sharkdp/bat/blob/master/CONTRIBUTING.md#add-an-entry-to-the-changelog