Change the default ‘C-c w’ and ‘C-c W’ key-bindings

Section 22.2.1 of the Emacs Lisp Manual, “Major Mode Conventions,”
says the following about keys:

    The key sequences bound in a major mode keymap should usually
    start with ‘C-c’, followed by a control character, a digit, or
    ‘{’, ‘}’, ‘<’, ‘>’, ‘:’ or ‘;’.  The other punctuation characters
    are reserved for minor modes, and ordinary letters are reserved
    for users.

Users should be able to safely use a key sequence such as ‘C-c w’
without concern for conflicts with any major mode.  However, Wiki Nav
Mode violates that reservation.  Therefore, this patch changes

    C-c w    ->    C-c C-w
    C-c W    ->    C-c C-W

in order to avoid conflicts with users’ keys.
Merge pull request #2 from ejmr/ejmr/rebind-find-link-keys

Change the default ‘C-c w’ and ‘C-c W’ key-bindings
doc change to key bindings
respect comments in any child of prog-mode

prog-mode is a recent addition to Emacs
use Ubuntu Emacs Lisp PPA for snapshot
revert to Cassou PPA for Emacs 24 (stable)
travis: remove emacs-snapshot-gtk package
update copyright

meaningless change to kick travis