[RFC] Remove `~` after end-of-line

Hey,

this replaces the `~` shown after the last line in the file by a space.

I'd argue that this character is rather useless and many people either just put up with it or change the `NonText` highlight group so that foreground and background have the same color. But the problem with the latter _solution_ is that `NonText` also gets used for some characters from the `'listchars'` option where it would be useful to actually see them.. :-)

Alternatively, one could create an own highlight group for it.

I'm not sure how compatible you'd like to stay with Vim, but this always bugged me somehow:

http://i.imgur.com/q2EEFoo.png

p.s. At the moment the fold and sign columns get continued after the last line, too. I could patch them out, if wanted. IMHO there's no reason to show anything after the end of the actual file.