Windows: Workaround for long paths (#23)

By using the short path version of a file, we can
manage to move long paths to the trash.

Limitations:
1/ If the final short path is longer than what
    `SHFileOperationW` can handle, it will fail
2/ Still not able to trash long path from another
    drive, ie: trying to delete C:\temp\foo.txt
    while the script is running from D:\trash.py

tests/test_plat_win.py

@@ -0,0 +1,46 @@
+# coding: utf-8
+import os
+import sys
+import unittest
+from os import path as op
+from tempfile import gettempdir
+
+from send2trash import send2trash as s2t
+
+
+@unittest.skipIf(sys.platform != 'win32', 'Windows only')
+class TestLongPath(unittest.TestCase):
+    def setUp(self):
+        filename = 'A' * 100
+        self.dirname = '\\\\?\\' + os.path.join(gettempdir(), filename)
+        self.file = os.path.join(
+            self.dirname,
+            filename,
+            filename,  # From there, the path is not trashable from Explorer
+            filename,
+            filename + '.txt')
+        self._create_tree(self.file)
+
+    def tearDown(self):
+        try:
+            os.remove(self.dirname)
+        except OSError:
+            pass
+
+    def _create_tree(self, path):
+        dirname = os.path.dirname(path)
+        if not os.path.isdir(dirname):
+            os.makedirs(dirname)
+        with open(path, 'w') as writer:
+            writer.write('Looong filename!')
+
+    def test_trash_file(self):
+        s2t(self.file)
+        self.assertFalse(op.exists(self.file))
+
+    @unittest.skipIf(
+        op.splitdrive(os.getcwd())[0] != op.splitdrive(gettempdir())[0],
+        'Cannot trash long path from other drive')
+    def test_trash_folder(self):
+        s2t(self.dirname)
+        self.assertFalse(op.exists(self.dirname))