TOUCH command

Implement the TOUCH command and refactor several of our "variadic key"
commands, which were previously all using their own specific handlers.

While refactoring the code, I changed `EXISTS` to require one key (it
had previously been set to require zero keys).

Additonally, it looks like we had a disparity in two commands which
should be idential to PhpRedis:  SINTERSTORE and SUNIONSTORE.
Previously, SINTERSTORE required only one argument but SUNIONSTORE 2.

I simply changed SUNIONSTORE to also only require a single argument,
since that argument could be an array.

```php
$redis->sInterStore(['dst', 'src1', 'src2']);
$redis->sUnionStore(['dst', 'src1', 'src2']);
```

1 files changed, 17 insertions, 2 deletions

diff --git a/tests/RedisTest.php b/tests/RedisTest.php
index 028116b4..cd9f631b 100644
--- a/tests/RedisTest.php
+++ b/tests/RedisTest.php
@@ -894,8 +894,7 @@ class Redis_Test extends TestSuite
     }
 
 
-    public function testExists()
-    {
+    public function testExists() {
         /* Single key */
         $this->redis->del('key');
         $this->assertEquals(0, $this->redis->exists('key'));
@@ -917,6 +916,22 @@ class Redis_Test extends TestSuite
         $this->assertEquals(count($mkeys), call_user_func_array([$this->redis, 'exists'], $mkeys));
     }
 
+    public function testTouch() {
+        if (!$this->minVersionCheck('3.2.1'))
+            $this->markTestSkipped();
+
+        $this->redis->del('notakey');
+
+        $this->assertTrue($this->redis->mset(['{idle}1' => 'beep', '{idle}2' => 'boop']));
+        usleep(1100000);
+        $this->assertTrue($this->redis->object('idletime', '{idle}1') >= 1);
+        $this->assertTrue($this->redis->object('idletime', '{idle}2') >= 1);
+
+        $this->assertEquals(2, $this->redis->touch('{idle}1', '{idle}2', '{idle}notakey'));
+        $this->assertTrue($this->redis->object('idletime', '{idle}1') == 0);
+        $this->assertTrue($this->redis->object('idletime', '{idle}2') == 0);
+    }
+
     public function testKeys()
     {
         $pattern = 'keys-test-';