Properly handle newlines and missing titles

[heptal]

Textareas can return their content with DOS-style \r\n line endings. This happens in Chrome on OSX, among many other browsers and platforms. This makes the .md files rather cumbersome to work with in vim and other tools.

When editing, jingo currently splits the file content on \n newlines and then joins them again to a single blob. This loses existing newline data for .md files which use \n-style line endings, which happens to be most of them. Try editing README.md for an example.

This commit converts all line endings to \n on creation or the next edit of an existing file, preserving all newlines. It also allows jingo to properly edit existing Unix-style markdown files by less-destructively reading the file input.

The 2 followup commits allow you to add other markdown files without proper titles to jingo, as in the case of migrating from gollum. This is accomplished by checking for a jingo-formatted title line, making sure the first line of content does not get clobbered when editing, and using the filename for a title where appropriate. Subsequent edits prepend the jingo-formatted title to the file if necessary while staying compatible with other tools.

[claudioc]

That's great, very nice stuff. I already had an issue about line endings normalizing (I was aware of the problem). Two birds with a stone!

And I did not think about eventually importing data from other systems.

Thank you very much!