Show "no newline at end of file" warning

[dverbru]

Show "no newline at end of file" warning like in GitHub.

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Step 1: Describe the problem:

Often text editors add new lines at EOF to comply with UNIX standard as git expects. When such newlines are introduced (or accidentally removed) to an already tracked file, this diff viewer doesn't offer a visual clue about that missing invisible character. Please note that git-diff shows a warning for this case in the terminal and GitHub supports it on their diff viewer.

Steps to reproduce:

1. Create a text file that does not end with a new line character and commit it.
2. Add a new line at the end of that file and commit it.
3. Perform the diff with diff2html CLI.

Observed Results:

• The last line is correctly marked as changed, but it is not visible what exactly changed in there.

Expected Results:

• A "no newline at end of file" mark next the version missing it, like the one GitHub shows on their diff viewer.

[rtfpessoa]

@dverbru that makes complete sense. PRs are welcome 😄