add '--abort-on-skip' option and ability to control skip behavior

the 'skip' config option controls skipping behavior:
    true    - skip download if file already exist (default)
    false   - download and overwrite files even if it exists
    "abort" - abort extractor run if a download would be skipped
              (same as '--abort-on-skip')

gallery_dl/extractor/hbrowse.py

@@ -19,7 +19,7 @@ class HbrowseMangaExtractor(Extractor):
     subcategory = "manga"
     pattern = [r"(?:https?://)?(?:www\.)?hbrowse\.com/(\d+)/?$"]
     test = [("http://www.hbrowse.com/10363", {
-        "url": "b89682bfb86c11d2af0dc47463804ec3ac4aadd6",
+        "url": "4d9def5df21c23f8c3d36de2076c189c02ea43bd",
     })]
 
     def __init__(self, match):