Add "remove newline" option.

Newline characters can be useful when a wysiwyg editor is interpreting content saved into the database and rendering it to a logged in user.
If the content is exported (via views_datasource) into another device, which then takes the same content and renders it into a browser, or WebUIView, as is in the case with mobile applications, newline characters are not needed. Newline characters are not rendered natively by browsers, instead they rely on HTML and CSS.
If the content is exported into another device, but it is then rendered into a WYSIWYG view in that device, then newlines might be useful.

Since there can be different use cases with newline characters, I think it's best to let the user decide what he prefers best. I'm adding support for letting the user specify if he wants his content with newline characters or not. Note that this option will affect all the export fields, just like the Plaintext output option does.