Fix error with temp file read access on Windows

Attempting to access the temp file after creation on Windows will trigger Permission Error.
The fix is to set the the delete flag to False (which is a quick and dirty hack),
which allows Python to 'release' the file handle, resulting in successful subsequent read access under Windows.

Docs reference: https://docs.python.org/3/library/tempfile.html#tempfile.NamedTemporaryFile
`Whether the name can be used to open the file a second time, while the named temporary file is still open,
varies across platforms (it can be so used on Unix; it cannot on Windows NT or later)`

Fixes #255

src/pytesseract.py

@@ -164,7 +164,7 @@ def prepare(image):
 @contextmanager
 def save(image):
     try:
-        with NamedTemporaryFile(prefix='tess_') as f:
+        with NamedTemporaryFile(prefix='tess_', delete=False) as f:
             if isinstance(image, str):
                 yield f.name, realpath(normpath(normcase(image)))
                 return