Implement printer-side rendering of QR codes for printers that support it.

Expand settings on escpos.qr to include ec, size,
model and 'native' (send image or send esc/pos QR command).

Default is set as native=False, so existing code will continue to
render QR codes as images.

test/test_function_qr_native.py

@@ -0,0 +1,81 @@
+#!/usr/bin/python
+"""test native QR code printing
+
+:author: `Michael Billington <michael.billington@gmail.com>`_
+:organization: `python-escpos <https://github.com/python-escpos>`_
+:copyright: Copyright (c) 2016 `Michael Billington <michael.billington@gmail.com>`_
+:license: GNU GPL v3
+"""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+from nose.tools import with_setup
+
+import escpos.printer as printer
+import os
+from escpos.constants import QR_ECLEVEL_H, QR_MODEL_1
+
+devfile = 'testfile'
+
+
+def setup_testfile():
+    """create a testfile as devfile"""
+    fhandle = open(devfile, 'a')
+    try:
+        os.utime(devfile, None)
+    finally:
+        fhandle.close()
+
+
+def teardown_testfile():
+    """destroy testfile again"""
+    os.remove(devfile)
+
+
+@with_setup(setup_testfile, teardown_testfile)
+def test_function_qr_defaults():
+    """test QR code with defaults"""
+    instance = printer.File(devfile=devfile)
+    instance.qr("1234", native=True)
+    instance.flush()
+    with open(devfile, "rb") as f:
+        assert(f.read() == b'\x1d(k\x04\x001A2\x00\x1d(k\x03\x001C\x03\x1d(k\x03\x001E0\x1d(k\x07\x001P01234\x1d(k\x03\x001Q0')
+
+@with_setup(setup_testfile, teardown_testfile)
+def test_function_qr_empty():
+    """test QR printing blank code"""
+    instance = printer.File(devfile=devfile)
+    instance.qr("", native=True)
+    instance.flush()
+    with open(devfile, "rb") as f:
+        assert(f.read() == b'')
+
+@with_setup(setup_testfile, teardown_testfile)
+def test_function_qr_ec():
+    """test QR error correction setting"""
+    instance = printer.File(devfile=devfile)
+    instance.qr("1234", native=True, ec=QR_ECLEVEL_H)
+    instance.flush()
+    with open(devfile, "rb") as f:
+        assert(f.read() == b'\x1d(k\x04\x001A2\x00\x1d(k\x03\x001C\x03\x1d(k\x03\x001E3\x1d(k\x07\x001P01234\x1d(k\x03\x001Q0')
+
+@with_setup(setup_testfile, teardown_testfile)
+def test_function_qr_size():
+    """test QR box size"""
+    instance = printer.File(devfile=devfile)
+    instance.qr("1234", native=True, size=7)
+    instance.flush()
+    with open(devfile, "rb") as f:
+        assert(f.read() == b'\x1d(k\x04\x001A2\x00\x1d(k\x03\x001C\x07\x1d(k\x03\x001E0\x1d(k\x07\x001P01234\x1d(k\x03\x001Q0')
+
+@with_setup(setup_testfile, teardown_testfile)
+def test_function_qr_model():
+    """test QR model"""
+    instance = printer.File(devfile=devfile)
+    instance.qr("1234", native=True, model=QR_MODEL_1)
+    instance.flush()
+    with open(devfile, "rb") as f:
+        assert(f.read() == b'\x1d(k\x04\x001A1\x00\x1d(k\x03\x001C\x03\x1d(k\x03\x001E0\x1d(k\x07\x001P01234\x1d(k\x03\x001Q0')