Fix a bunch of ReST refs in the code

GitOrigin-RevId: ddfae7263e0edda4dc87083aa6babba998ecedcf
Change-Id: I4fb352f9f4b885fbb53730547e29b3f76b9743d2

code/png.py

diff --git a/code/png.py b/code/png.py
index 3782b3a..2afc3bc 100755
--- a/code/png.py
+++ b/code/png.py
@@ -1384,9 +1384,9 @@
     def undo_filter(self, filter_type, scanline, previous):
         """
         Undo the filter for a scanline.
-        `scanline` is a sequence of bytes that
+        *scanline* is a sequence of bytes that
         does not include the initial filter type byte.
-        `previous` is decoded previous scanline
+        *previous* is decoded previous scanline
         (for straightlaced images this is the previous pixel row,
         but for interlaced images, it is
         the previous scanline in the reduced image,
@@ -1825,9 +1825,9 @@
 
         May use excessive memory.
 
-        `values` is a single array.
+        *values* is a single array.
 
-        The :meth:`read` method is more stream-friendly than this,
+        The `read` method is more stream-friendly than this,
         because it returns a sequence of rows.
         """
 
@@ -1841,7 +1841,7 @@
         Returns a palette that is a sequence of 3-tuples or 4-tuples,
         synthesizing it from the ``PLTE`` and ``tRNS`` chunks.
         These chunks should have already been processed (for example,
-        by calling the :meth:`preamble` method).
+        by calling the `preamble` method).
         All the tuples are the same size:
         3-tuples if there is no ``tRNS`` chunk,
         4-tuples when there is a ``tRNS`` chunk.
@@ -1849,7 +1849,7 @@
         Assumes that the image is colour type
         3 and therefore a ``PLTE`` chunk is required.
 
-        If the `alpha` argument is ``'force'`` then an alpha channel is
+        If the *alpha* argument is ``'force'`` then an alpha channel is
         always added, forcing the result to be a sequence of 4-tuples.
         """
 
@@ -1875,7 +1875,7 @@
         the colour value directly without needing to refer
         to palettes or transparency information.
 
-        Like the :meth:`read` method this method returns a 4-tuple:
+        Like the `read` method this method returns a 4-tuple:
 
         (*width*, *height*, *rows*, *info*)
 
@@ -1883,7 +1883,7 @@
         the bit depth they have in the source image.
 
         The *info* dictionary that is returned reflects
-        the `direct` format and not the original source image.
+        the *direct* format and not the original source image.
         For example, an RGB source image with a ``tRNS`` chunk
         to represent a transparent colour,
         will start with ``planes=3`` and ``alpha=False`` for the