Move while stmt from block stmt 2 keywords to other in emacs major mode.

Make while an other keyword (c-other-kwds) in emacs major mode instead of block
stmt with 2 keywords (c-block-stmt-2-kwds). Before this change, the indentation
for the block of while loops that did not surround the conditional in
parenthesis was broken.

This while loop shows the issue. Before the fix, this is the indentation:

```chpl
while (x % 2 != 1) {
  writeln("nothing");
 }
while x % 2 != 1 {
  writeln("nothing");
          }
```

With this fix, the indentation is correct with and without parens:

```chpl
while (x % 2 != 1) {
  writeln("nothing");
}
while x % 2 != 1 {
  writeln("nothing");
}
```

In addition to this fix, the `chpl-mode.el` file that was copied into the 22/ and 23/ directories now
lives at `etc/emacs/`. For backward compatibility, there are symlinks in the 22/ and 23/ dirs. The
README includes updated instructions based on the new file location.

### TODO:

* [x] Verify indentation is correct on more complex programs with while loops.
* [x] Verify symlinks in `etc/emacs/{22,23}/chpl-mode.el` still work.
* [x] Verify updated emacs-lisp snippet works in `init.el`/`.emacs`.
* [x] Verify it is OK to migrate README to rst format. See rendered version here: https://github.com/thomasvandoren/chapel/blob/update-while-stmt-in-emacs-mode/etc/emacs/README.rst#chapel-emacs-mode