Improve and simplify titling functions.

Multiplexer titles can be set independent of window and tab titles.
Add auto-title always option to have dynamic titling inside terminal
multiplexers. Setting auto-title to yes continues to ignore dynamic
titling inside terminal multiplexers.

This patch should not alter behavior under Apple terminals.

modules/terminal/README.md

@@ -13,14 +13,19 @@ directory, add the following to *zpreztorc*:
 
     zstyle ':prezto:module:terminal' auto-title 'yes'
 
-Auto titling is disabled inside terminal multiplexers, except inside dvtm, since
-it interferes with window names defined in configuration files and profile
-managers.
+Auto titling is disabled inside terminal multiplexers (except inside dvtm)
+since it interferes with window names defined in configuration files and
+profile managers. This can be overridden by setting it to `always`.
+
+    zstyle ':prezto:module:terminal' auto-title 'always'
+
+### Title formats
 
 To format terminal window and tab titles, add the following to *zpreztorc*:
 
     zstyle ':prezto:module:terminal:window-title' format '%n@%m: %s'
     zstyle ':prezto:module:terminal:tab-title' format '%m: %s'
+    zstyle ':prezto:module:terminal:multiplexer-title' format '%s'
 
 `%s` will be replaced with the current working directory path or the currently
 executing program name.
@@ -31,7 +36,8 @@ Functions
 ---------
 
 - `set-tab-title` sets the terminal tab title.
-- `set-window-title` sets the terminal or terminal multiplexer window title.
+- `set-window-title` sets the terminal window title.
+- `set-multiplexer-title` sets the terminal multiplexer title.
 
 Authors
 -------
@@ -39,6 +45,7 @@ Authors
 *The authors of this module should be contacted via the [issue tracker][2].*
 
   - [Sorin Ionescu](https://github.com/sorin-ionescu)
+  - [Olaf Conradi](https://github.com/oohlaf)
 
 [1]: http://zsh.sourceforge.net/Doc/Release/Prompt-Expansion.html#Expansion-of-Prompt-Sequences
 [2]: https://github.com/sorin-ionescu/prezto/issues