Org writer: Fix output for linebreaks

Hard linebreaks in Org mode are represented by the string "\\" as the
last characters in a line.  Adds this feature to the Org-mode writer.
Org reader: Read linebreaks

Linebreaks are marked by the string `\\` at the end of a line.
Fix editorconfig for test files

Test output files should be exactly as defined with regard to trailing
whitespace.  This keeps editorconfig from breaking those files.
Merge pull request #1239 from tarleb/org-linebreak

Org linebreaks