Add --no-verbose option

The action for "--verbose" has been changed to BooleanOptionalAction,
which adds a negative version that may be useful for overriding
configuration files.

bonemarketsolver/__main__.py

@@ -105,7 +105,7 @@ solver_options = parser.add_argument_group(
 
 solver_options.add_argument(
         "-v", "--verbose",
-        action='store_true',
+        action=argparse.BooleanOptionalAction,
         default=False,
         help="whether the solver should output search progress rather than showing intermediate solutions",
         dest='verbose'