Add note about .emacs.d Windows path

At least on my Windows 7 machine, `user-emacs-directory` prints `~/.emacs.d`, which is not really useful, since you also then have to realize that the tilde refers to the roaming appdata directory. I think this way of documenting would perhaps be more immediately useful. For probably almost all other platforms the tilde path will work just fine.
Add instructions for getting homedir path

This should work for all versions of Windows.
Clean up `prelude-cleanup-buffer` code

- Create a macro `with-region-or-buffer` to replace the prelude wrapper
  around `untabify` and `indent-region`
- Remove the function operated on buffers, cause we only need the dwim
  one
Do not indent region with indent sensitive modes

- Rename and move yank indent vars into prelude-custom.el
- Add coffee-mode to prelude-indent-sensitive-modes
- Do not mess up indentation when cleanup with indentation sensitive
  modes, such as Python.
Remove duplication advice of yank and yank-pop
Do not bind "C-c i" to slime-inspect

This keybinding is in conflict with that of `prelude-ido-goto-symbol`,
and `slime-inspect` is already bound to "C-c I"
Start slime automatically with `slime-auto-start`
Merge pull request #590 from toctan/slime

Start slime automatically via `slime-auto-start`
Merge pull request #584 from toctan/cleanup-buffer

Cleanup code of `prelude-cleanup-buffer`
Merge pull request #571 from ilkka/patch-1

Add note about .emacs.d Windows path