Replace'flet' with a combination of 'let' and 'lambda'.
'flet' has been obsoleted on Emacs 24.3.

* twittering-mode.el: Remove 'flet'.
(twittering-normalize-raw-status): replace 'flet' with a
combination of 'let' and 'lambda'.
Add marks and a script for updating CA certificates automatically.

* twittering-mode.el: Add marks and a script for updating CA
certificates automatically.
(twittering-ca-cert-list): add marks for updating CA certificates
automatically.
* update-cert.sh: Add a script to update CA certificates
automatically. This script retrieves certificates distributed on
the site of cURL.
* cert/*: Removed.
Update embedded CA certificates.

* twittering-mode.el: Update embedded CA certificates.
(twittering-ca-cert-list): update CA certificates.
Replace images that had been retrieved from other softwares.

* twittering-mode.el: Replace images that had been imported from
other softwares.
(twittering-ssl-indicator-image): replaced with an original
image.
(twittering-active-indicator-image): likewise.
(twittering-inactive-indicator-image): likewise.