varstash integration

Fixes: https://github.com/Tarrasch/zsh-autoenv/issues/5

tests/varstash.t

@@ -0,0 +1,36 @@
+Test varstash integration.
+
+  $ source $TESTDIR/setup.sh
+
+Setup test environment.
+
+# Defaults:
+# $ DOTENV_FILE_ENTER=.env
+# $ DOTENV_FILE_LEAVE=.env.leave
+# $ DOTENV_HANDLE_LEAVE=1
+
+  $ mkdir sub
+  $ cd sub
+  $ echo "autostash FOO=baz" > $DOTENV_FILE_ENTER
+  $ echo "autounstash" > $DOTENV_FILE_LEAVE
+
+Manually create auth file
+
+  $ echo "$PWD/$DOTENV_FILE_ENTER:$(echo $(<$DOTENV_FILE_ENTER) | shasum)" > $ENV_AUTHORIZATION_FILE
+  $ echo "$PWD/$DOTENV_FILE_LEAVE:$(echo $(<$DOTENV_FILE_LEAVE) | shasum)" >> $ENV_AUTHORIZATION_FILE
+
+Set environment variable.
+
+  $ FOO=bar
+
+Activating the env stashes it and applies a new value.
+
+  $ cd .
+  $ echo $FOO
+  baz
+
+Leaving the directory unstashes it.
+
+  $ cd ..
+  $ echo $FOO
+  bar