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.

src/nvim/ex_docmd.c

@@ -5375,9 +5375,7 @@ static void ex_hide(exarg_T *eap)
  */
 static void ex_stop(exarg_T *eap)
 {
-  /*
-   * Disallow suspending for "rvim".
-   */
+  // Disallow suspending in restricted mode (-Z)
   if (!check_restricted()) {
     if (!eap->forceit) {
       autowrite_all();