Insert a final newline if needed

[lhecker]

• Detects any final newline on open
• ...otherwise assumes "false" on Windows
• If there was a final newline, we now insert one automatically
  if the user wrote something at the end of the file

Closes #41

[jantari]

I'm curious, what is the story of no final newline on Windows? I thought having the final newline was the universally correct way to write / save a text file on all platforms.

[DHowett]

@jantari If you want all the terrible terrible details, read #41 - people are very upset about it ;P

[lhecker]

The same applies to the default line endings, which are also CRLF on Windows and LF anywhere else. I personally have set up all my editors to use LF and produce a final newline, but people don't like that.

The upside of this approach is that it appears to work quite well at least on existing files.

[jantari]

Well, for this editor at least (being simple, approachable, built-in), not changing it in existing files is certainly the best choice. No final newline in new files looks to mostly be the opinion of one very upset individual there, but oh well. I realize this PR is not the place to harp on that and a decision has been made. Thanks for the link and comments.