add extractors for gelbooru v0.1 sites

- support https://illusioncards.booru.org/  (closes #426)
- support https://the-collection.booru.org/ (closes #767)
- support https://allgirl.booru.org/
- closes #234, closes #473, closes #1238

To get gallery-dl to recognize other sites running Gelbooru v0.1
(most sites on booru.org), add one or more entries to the
'gelbooru_v01' block in your config file. For example:

{
    "extractor": {
        "gelbooru_v01": {
            "rozenmaidenbooru": {"root": "http://rm.booru.org"},
            "drawfriendsbooru": {"root": "http://drawfriends.booru.org"}
        }
    }
}

gallery_dl/extractor/__init__.py

@@ -35,6 +35,7 @@
     "furaffinity",
     "fuskator",
     "gelbooru",
+    "gelbooru_v01",
     "gelbooru_v02",
     "gfycat",
     "hbrowse",

gallery_dl/extractor/gelbooru_v01.py

@@ -0,0 +1,143 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2021 Mike Fährmann
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+"""Extractors for Gelbooru v0.1 sites"""
+
+from . import booru
+from .. import text
+
+
+class GelbooruV01Extractor(booru.BooruExtractor):
+    basecategory = "gelbooru_v01"
+    per_page = 20
+
+    def _parse_post(self, post_id):
+        url = "{}/index.php?page=post&s=view&id={}".format(
+            self.root, post_id)
+        page = self.request(url).text
+
+        post = text.extract_all(page, (
+            ("created_at", 'Posted: ', ' <'),
+            ("uploader"  , 'By: ', ' <'),
+            ("width"     , 'Size: ', 'x'),
+            ("height"    , '', ' <'),
+            ("source"    , 'Source: <a href="', '"'),
+            ("rating"    , 'Rating: ', '<'),
+            ("score"     , 'Score: ', ' <'),
+            ("file_url"  , '<img alt="img" src="', '"'),
+            ("tags"      , 'id="tags" name="tags" cols="40" rows="5">', '<'),
+        ))[0]
+
+        post["id"] = post_id
+        post["md5"] = post["file_url"].rpartition("/")[2].partition(".")[0]
+        post["rating"] = (post["rating"] or "?")[0].lower()
+        post["tags"] = text.unescape(post["tags"])
+        post["date"] = text.parse_datetime(
+            post["created_at"], "%Y-%m-%d %H:%M:%S")
+
+        return post
+
+
+BASE_PATTERN = GelbooruV01Extractor.update({
+    "thecollection"     : {"root": "https://the-collection.booru.org"},
+    "illusioncardsbooru": {"root": "https://illusioncards.booru.org"},
+    "allgirlbooru"      : {"root": "https://allgirl.booru.org"},
+})
+
+
+class GelbooruV01TagExtractor(GelbooruV01Extractor):
+    subcategory = "tag"
+    directory_fmt = ("{category}", "{search_tags}")
+    archive_fmt = "t_{search_tags}_{id}"
+    pattern = BASE_PATTERN + r"/index\.php\?page=post&s=list&tags=([^&#]+)"
+    test = (
+        (("https://the-collection.booru.org"
+          "/index.php?page=post&s=list&tags=parody"), {
+            "range": "1-25",
+            "count": 25,
+        }),
+        (("https://illusioncards.booru.org"
+          "/index.php?page=post&s=list&tags=koikatsu"), {
+            "range": "1-25",
+            "count": 25,
+        }),
+        ("https://allgirl.booru.org/index.php?page=post&s=list&tags=dress", {
+            "range": "1-25",
+            "count": 25,
+        }),
+    )
+
+    def __init__(self, match):
+        GelbooruV01Extractor.__init__(self, match)
+        self.tags = match.group(match.lastindex)
+
+    def metadata(self):
+        return {"search_tags": text.unquote(self.tags.replace("+", " "))}
+
+    def posts(self):
+        url = "{}/index.php?page=post&s=list&tags={}&pid=".format(
+            self.root, self.tags)
+        pid = self.page_start
+
+        while True:
+            page = self.request(url + str(pid)).text
+
+            cnt = 0
+            for post_id in text.extract_iter(
+                    page, 'class="thumb"><a id="p', '"'):
+                yield self._parse_post(post_id)
+                cnt += 1
+
+            if cnt < self.per_page:
+                return
+            pid += self.per_page
+
+
+class GelbooruV01PostExtractor(GelbooruV01Extractor):
+    subcategory = "post"
+    archive_fmt = "{id}"
+    pattern = BASE_PATTERN + r"/index\.php\?page=post&s=view&id=(\d+)"
+    test = (
+        (("https://the-collection.booru.org"
+          "/index.php?page=post&s=view&id=100520"), {
+            "url": "0329ac8588bb93cf242ca0edbe3e995b4ba554e8",
+            "content": "1e585874e7b874f7937df1060dd1517fef2f4dfb",
+        }),
+        (("https://illusioncards.booru.org"
+          "/index.php?page=post&s=view&id=82746"), {
+            "url": "3f9cd2fadf78869b90bc5422f27b48f1af0e0909",
+            "content": "159e60b92d05597bd1bb63510c2c3e4a4bada1dc",
+        }),
+        ("https://allgirl.booru.org/index.php?page=post&s=view&id=107213", {
+            "url": "b416800d2d2b072f80d3b37cfca9cb806fb25d51",
+            "content": "3e3c65e0854a988696e11adf0de52f8fa90a51c7",
+            "keyword": {
+                "created_at": "2021-02-13 16:27:39",
+                "date": "dt:2021-02-13 16:27:39",
+                "file_url": "https://img.booru.org/allgirl//images/107"
+                            "/2aaa0438d58fc7baa75a53b4a9621bb89a9d3fdb.jpg",
+                "height": "1200",
+                "id": "107213",
+                "md5": "2aaa0438d58fc7baa75a53b4a9621bb89a9d3fdb",
+                "rating": "s",
+                "score": str,
+                "source": None,
+                "tags": "blush dress green_eyes green_hair hatsune_miku "
+                        "long_hair twintails vocaloid",
+                "uploader": "Honochi31",
+                "width": "1600"
+            },
+        }),
+    )
+
+    def __init__(self, match):
+        GelbooruV01Extractor.__init__(self, match)
+        self.post_id = match.group(match.lastindex)
+
+    def posts(self):
+        return (self._parse_post(self.post_id),)