support -B option

problem2html.patch

--- a/src/problem2html.py
+++ b/src/problem2html.py
@@ -110,6 +110,8 @@ class ConvertOptions:
          'set title (only used when there is no pre-existing template and -h not set).'],
         ['loglevel', 'store', '-L', '--log-level',
          'set log level (debug, info, warning, error, critical).'],
+        ['imgbasedir', 'store', '-B', '--image-base-dir',
+         'set image base directory'],
         ['quiet', 'store_true', '-q', '--quiet',
          "quiet."],
         ]