Interface cleanup: Symlink handling & docs

This removes the ability to start nvim via the following aliases in
favor of just using their command line arguments:

ex        vim -e
exim      vim -E
view      vim -R
gvim      vim -g
gex       vim -eg
gview     vim -Rg
rvim      vim -Z
rview     vim -RZ
rgvim     vim -gZ
rgview    vim -RgZ

This also removes Vi mode (-v) for consistency. From ':help -v':

    -v  Start Ex in Vi mode.  Only makes a difference when the
    executable is called "ex" or "gvim".  For gvim the GUI is not
    started if possible.

runtime/syntax/dirpager.vim

@@ -14,7 +14,7 @@
 " License:	  VIM License
 "		  Vim is Charityware, see ":help Uganda"
 "
-" Usage:	  $ ls -la | view -c "set ft=dirpager" -
+" Usage:	  $ ls -la | nvim -R -c "set ft=dirpager" -
 "
 "
 ",----[ ls(1posix) ]--------------------------------------------------