Don't clutter Echo Area

* lv.el (lv-wnd): New variable.
(lv-window): New defun to get a window similar in properties to Echo Area.
(lv-message): New defun, a replacement for `message', that writes to `lv-window'.

* hydra.el (hydra-lv): New defcustom. If nil, use the Echo Area,
  otherwise, use LV.
(hydra-disable): Add optional arg KILL-LV.
(hydra--message): New defun to dispatch on `hydra-lv'.
(hydra--make-defun): Prematurely disable with LV only for blue heads,
since regenerating LV window would cause screen tearing. No need for
timeouts between `message' when using LV.  HINT argument is now a
function symbol that returns a string, instead of a plain string.
(defhydra): Generate a new defun with name `NAME/hint'.

* Makefile: Load lv.

* hydra-test.el: Update all tests.

* README.md: Update.

Makefile

@@ -1,7 +1,7 @@
 EMACS = emacs
 # EMACS = emacs-24.3
 
-LOAD = -l hydra.el -l hydra-test.el
+LOAD = -l lv.el -l hydra.el -l hydra-test.el
 
 .PHONY: all test clean
 

README.md

@@ -266,3 +266,14 @@ to a head. This sexp will be wrapped in an interactive lambda. Here's an example
    ("q" nil "cancel"))
 (global-set-key (kbd "C-c r") 'hydra-launcher/body)
 ```
+
+## Define Hydra heads that don't show up in the hint at all
+
+This can be done by setting the head's hint explicitly to `nil`, instead of the usual string.
+
+## Use a dedicated window for Hydra hints
+
+Since version `0.10.0`, setting `hydra-lv` to `t` (the default setting) will make it use a dedicated
+window right above the Echo Area for hints. This has the advantage that you can immediately see
+any `message` output from the functions that you call, since Hydra no longer uses `message` to display
+the hint. You can still have the old behavior by setting `hydra-lv` to `nil`.