Fix the comments about the storage for the image.

Some of the comments that talk about the storage for the descriptor
(the aom_image_t struct) are actually actually referring to the storage
for the image (the memory buffer pointed to by the img_data field in
aom_image_t).

Change-Id: I67fbe1e092f49cf35f5ac3aa6b7b2b3f1f9d3a9d
diff --git a/aom/aom_image.h b/aom/aom_image.h
index 245ef2c..bc0c6a6 100644
--- a/aom/aom_image.h
+++ b/aom/aom_image.h
@@ -202,7 +202,7 @@
 /*!\brief Open a descriptor, allocating storage for the underlying image
  *
  * Returns a descriptor for storing an image of the given format. The
- * storage for the descriptor is allocated on the heap.
+ * storage for the image is allocated on the heap.
  *
  * \param[in]    img       Pointer to storage for descriptor. If this parameter
  *                         is NULL, the storage for the descriptor will be
@@ -211,7 +211,7 @@
  * \param[in]    d_w       Width of the image
  * \param[in]    d_h       Height of the image
  * \param[in]    align     Alignment, in bytes, of the image buffer and
- *                         each row in the image(stride).
+ *                         each row in the image (stride).
  *
  * \return Returns a pointer to the initialized image descriptor. If the img
  *         parameter is non-null, the value of the img parameter will be
@@ -224,7 +224,7 @@
 /*!\brief Open a descriptor, using existing storage for the underlying image
  *
  * Returns a descriptor for storing an image of the given format. The
- * storage for descriptor has been allocated elsewhere, and a descriptor is
+ * storage for the image has been allocated elsewhere, and a descriptor is
  * desired to "wrap" that storage.
  *
  * \param[in]    img       Pointer to storage for descriptor. If this parameter
@@ -233,7 +233,8 @@
  * \param[in]    fmt       Format for the image
  * \param[in]    d_w       Width of the image
  * \param[in]    d_h       Height of the image
- * \param[in]    align     Alignment, in bytes, of each row in the image.
+ * \param[in]    align     Alignment, in bytes, of each row in the image
+ *                         (stride).
  * \param[in]    img_data  Storage to use for the image
  *
  * \return Returns a pointer to the initialized image descriptor. If the img
@@ -248,7 +249,7 @@
  * border
  *
  * Returns a descriptor for storing an image of the given format and its
- * borders. The storage for the descriptor is allocated on the heap.
+ * borders. The storage for the image is allocated on the heap.
  *
  * \param[in]    img        Pointer to storage for descriptor. If this parameter
  *                          is NULL, the storage for the descriptor will be
@@ -257,7 +258,7 @@
  * \param[in]    d_w        Width of the image
  * \param[in]    d_h        Height of the image
  * \param[in]    align      Alignment, in bytes, of the image buffer and
- *                          each row in the image(stride).
+ *                          each row in the image (stride).
  * \param[in]    size_align Alignment, in bytes, of the image width and height.
  * \param[in]    border     A border that is padded on four sides of the image.
  *