Add autoenv, automatic environment setup

Using a hook, automatically detect when `.enter` and `.exit` scripts
and source them when changing the shells current directory.

autoenv/autoenv.plugin.zsh

@@ -66,8 +66,8 @@ _autoenv_exit() {
   _autoenv_entered[${_autoenv_entered[(i)$entered]}]=()
 }
 
-# Find a directory containing a .enter file by searching up the directory tree
-# starting in the current directory.
+# Find all directories containing a .enter file by searching up the directory
+# tree starting in the current directory.
 _autoenv_find_enter_directories() {
   local current=$PWD
   # If an enter script is found in the current directory, return it.
@@ -78,7 +78,8 @@ _autoenv_find_enter_directories() {
     local next=$current/..; local next=${next:A}
     # If an enter script is found in the current directory, return it.
     [ -f $next/.enter ] && echo $next
-    # If the current directory equals the next directory, return.
+    # If the current directory equals the next directory we are done, otherwise
+    # update the current directory.
     [[ $current == $next ]] && return || local current=$next
   done
 }