hydra 0.5.0

This release introduces colorful Hydra heads. Now, each head is:

• either red - calling this head will not vanquish the Hydra. This is the default one, and
  is exactly the same as the previous behavior
• or blue - calling this head will vanquish the Hydra.

You can mix-and-match the colors, if you like.

Here's an example of a pure-blue Hydra:

(global-set-key
 (kbd "C-c C-v")
 (defhydra toggle (:color blue)
   "toggle"
   ("a" abbrev-mode "abbrev")
   ("d" toggle-debug-on-error "debug")
   ("f" auto-fill-mode "fill")
   ("t" toggle-truncate-lines "truncate")
   ("w" whitespace-mode "whitespace")
   ("q" nil "cancel")))

Here's an almost all-red Hydra, with one blue head:

(defhydra hydra-error (global-map "M-g")
  "goto-error"
  ("h" first-error "first")
  ("j" next-error "next")
  ("k" previous-error "prev")
  ("v" recenter-top-bottom "recenter")
  ("q" nil "quit"))

The q became blue, because its function is nil.
Or, for example, you could make the first head also blue:

(defhydra hydra-error (global-map "M-g")
  "goto-error"
  ("h" first-error "first" :color blue)
  ("j" next-error "next")
  ("k" previous-error "prev")
  ("v" recenter-top-bottom "recenter")
  ("q" nil "quit"))

The advantages of a pure-blue Hydra over a plain nested keymap:

• You get a hint straight away, e.g. after C-c C-v

  toggle: [a]: abbrev, [d]: debug, [f]: fill, [t]: truncate, [w]: whitespace, [q]: cancel.
  

• You can still cancel C-c C-v with any other command.