Update docs for eventual v4.4 release

RELEASE_NOTES.rst

@@ -3,6 +3,23 @@ RELEASE NOTES
 
 OCRmyPDF uses `semantic versioning <http://semver.org/>`_.
 
+v4.4:
+=====
+
+-  Tesseract 4.00 is now supported on an experimental basis.
+
+   +  A new rendering option ``--pdf-renderer tess4`` exploits Tesseract 4's new text-only output PDF mode. See the documentation on PDF Renderers for details.
+   +  The ``--tesseract-oem`` argument allows control over the Tesseract 4 OCR 
+   engine mode.
+   +  Fixed poor performance with Tesseract 4.00 on Linux
+
+-  Fixed an issue that caused corruption of output to stdout in some cases
+-  Removed test for Pillow JPEG and PNG support, as the minimum supported version of Pillow now enforces this
+-  Significant code reorganization to make OCRmyPDF re-entrant and improve performance. All changes should be backward compatible for the v4.x series.
+
+   + However, OCRmyPDF's dependency "ruffus" is not re-entrant, so no Python API is available. Scripts should continue to use the command line interface.
+
+
 v4.3.5:
 =======
 

docs/index.rst

@@ -20,6 +20,7 @@ Contents:
    installation
    languages
    cookbook
+   renderers
    security
    errors
 

docs/installation.rst

@@ -262,7 +262,7 @@ where /c/Users/sampleuser is a Unix representation of the Windows path C:\\Users
 Installing HEAD revision from sources
 -------------------------------------
 
-If you have ``git`` and ``python3.4`` or ``python3.5`` installed, you can install from source. When the ``pip`` installer runs,
+If you have ``git`` and Python 3.4 or newer installed, you can install from source. When the ``pip`` installer runs,
 it will alert you if dependencies are missing.
 
 To install the HEAD revision from sources in the current Python 3 environment:

docs/security.rst

@@ -14,7 +14,7 @@ PDF is a rich, complex file format. The official PDF 1.7 specification, ISO 3200
 
 In short, PDFs `may contain viruses <https://security.stackexchange.com/questions/64052/can-a-pdf-file-contain-a-virus>`_.
 
-This `article <https://theinvisiblethings.blogspot.ca/2013/02/converting-untrusted-pdfs-into-trusted.html>`_ describes a method which allows potentially hostile PDFs to be viewed and rasterized safely in a disposable virtual machine. A trusted PDF created in this manner is converted to images and loses all information making it searchable. OCRmyPDF could be used restore searchability.
+This `article <https://theinvisiblethings.blogspot.ca/2013/02/converting-untrusted-pdfs-into-trusted.html>`_ describes a high-paranoia method which allows potentially hostile PDFs to be viewed and rasterized safely in a disposable virtual machine. A trusted PDF created in this manner is converted to images and loses all information making it searchable and losing all compression. OCRmyPDF could be used restore searchability.
 
 How OCRmyPDF processes PDFs
 ---------------------------