ture(escpos) Add buzzer function

- Add `buzzer(time, duration)` function to control the buzzer on supported
printers.
- Add unit tests for buzzer function.

test/test_function_buzzer.py

@@ -0,0 +1,46 @@
+import six
+import pytest
+
+from escpos import printer
+from escpos.constants import BUZZER
+
+
+def test_buzzer_function_with_default_params():
+    instance = printer.Dummy()
+    instance.buzzer()
+    expected = BUZZER + six.int2byte(2) + six.int2byte(4)
+    assert instance.output == expected
+
+
+@pytest.mark.parametrize(
+    "times, duration",
+    [
+        [1, 1], [2, 2], [3, 3], [4, 4], [5, 5], [6, 6], [7, 7], [8, 8], [9, 9],
+    ]
+)
+def test_buzzer_function(times, duration):
+    instance = printer.Dummy()
+    instance.buzzer(times, duration)
+    expected = BUZZER + six.int2byte(times) + six.int2byte(duration)
+    assert instance.output == expected
+
+
+@pytest.mark.parametrize(
+    "times, duration, expected_message",
+    [
+        [0, 0, "times must be between 1 and 9"],
+        [-1, 0, "times must be between 1 and 9"],
+        [10, 0, "times must be between 1 and 9"],
+        [11, 0, "times must be between 1 and 9"],
+        [3, 0, "duration must be between 1 and 9"],
+        [3, -1, "duration must be between 1 and 9"],
+        [3, 10, "duration must be between 1 and 9"],
+        [3, 11, "duration must be between 1 and 9"],
+    ]
+)
+def test_buzzer_fuction_with_outrange_values(times, duration, expected_message):
+    instance = printer.Dummy()
+    with pytest.raises(ValueError) as e:
+        instance.buzzer(times, duration)
+
+    assert str(e.value) == expected_message