Update documents

* README.md: Remove links to Debian snapshot since are not maintained
  anymore.
* tips.org: Add steps to build emacs from source on Mac OS X.
Remove frame operations

Emacs 24.4 has built-in `toggle-frame-maximized' and
`toggle-frame-fullscreen'.
Fix hunspell English dictionary could not be found

(ispell-find-hunspell-dictionaries) could not parse the output of
`hunspell -D' for en_US dictionary when the environment variables LANG
or LC_ALL is not been set in Emacs. It could only find dictionary whose
name is "default". Either rename dictionary files to "default", or set
LANG or LC_ALL to en_US could resolve this issue.

If hunspell is not installed, fall back to ispell.
Switch between two recently used buffers C-x C-b

Original (ibuffer) is rarely used.
Auto save buffer to the file for every 5 seconds
Refine whitespace mode settings

Use (delete-trailing-whitespace) instead (whitespace-cleanup) to remove
trailing whitespaces.
Support kill buffer without asking by C-x C-k
Rebind (magit-status) to F4
Remove (revert-buffer) keybinding

(global-auto-revert-mode) has been enabled.
Adjust (smex) and desktop keybindings

(smex) is frequently used which deserves a special key. Bind (smex) to
F12, and rebind (desktop-save) to F9.