Add command 'setcover'.

epubfile.py

@@ -1627,6 +1627,11 @@ def normalize_argparse(args):
         pipeable.stdout(epub.absolute_path)
     return 0
 
+def setcover_argparse(args):
+    book = Epub(args.epub)
+    book.set_cover_image(args.cover_id)
+    return 0
+
 def setfont(book, new_font, autoyes=False):
     css_id = 'epubfile_setfont'
     css_basename = 'epubfile_setfont.css'
@@ -1927,6 +1932,24 @@ def main(argv):
 
     ################################################################################################
 
+    p_setcover = subparsers.add_parser(
+        'setcover',
+        description='''
+        Set the book's cover image to the specified manifest ID.
+
+        You can use the manifest command first to see what's in the book.
+        ''',
+    )
+    p_setcover.add_argument(
+        'epub',
+    )
+    p_setcover.add_argument(
+        'cover_id',
+    )
+    p_setcover.set_defaults(func=setcover_argparse)
+
+    ################################################################################################
+
     p_setfont = subparsers.add_parser(
         'setfont',
         description='''