issue #523: keep newlines or set them globally to crlf or lf


Newline behaviour is made an option in coder -> preferences. It has three possible values:

* keep (the default), keep the type of newlines that the file had when opening, except when they where mixed or the file starts with #!, then use unix. For new files the system default is used.
* unix, use lf as newline
* dos, use crlf as newline

note that because of the use of universal newlines 'show EOL' will now always show LF since this is the standard newline in python strings.