FR: Robust option for fread not to split lines

[MichaelChirico]

As documented here, fread can be used rather effectively as a tool for reading fixed-width files within its existing framework.

One problem with using sep = "\n", however, is that carriage return is not so uniform across systems/file types (notably, Windows, with uses \r\n).

@dselivanov's PR # 1518 currently addresses this; I'm adding my hat in the ring to vouch for its utility.

There are other uses for this besides reading fixed-width files, but that is the application I see as having the most frequent benefit.

[MichaelChirico]

Closed by #2451