Make releasedata.Product usable in 'with' expression (#294)

This way the writing of the JSON file is handled automatically if the update does not fail.
It pave the way to further global improvements, such as a better error handling.

src/unrealircd.py

@@ -5,19 +5,17 @@ from common import dates, endoflife, http, releasedata
 
 DATE_PATTERN = re.compile(r"\d{4}-\d{2}-\d{2}")
 
-product = releasedata.Product("unrealircd")
-response = http.fetch_url("https://www.unrealircd.org/docwiki/index.php?title=History_of_UnrealIRCd_releases&action=raw")
-wikicode = mwparserfromhell.parse(response.text)
+with releasedata.ProductData("unrealircd") as product_data:
+    response = http.fetch_url("https://www.unrealircd.org/docwiki/index.php?title=History_of_UnrealIRCd_releases&action=raw")
+    wikicode = mwparserfromhell.parse(response.text)
 
-for tr in wikicode.ifilter_tags(matches=lambda node: node.tag == "tr"):
-    items = tr.contents.filter_tags(matches=lambda node: node.tag == "td")
-    if len(items) < 2:
-        continue
+    for tr in wikicode.ifilter_tags(matches=lambda node: node.tag == "tr"):
+        items = tr.contents.filter_tags(matches=lambda node: node.tag == "td")
+        if len(items) < 2:
+            continue
 
-    version = items[0].__strip__()
-    date_str = items[1].__strip__()
-    if endoflife.DEFAULT_VERSION_PATTERN.match(version) and DATE_PATTERN.match(date_str):
-        date = dates.parse_date(date_str)
-        product.declare_version(version, date)
-
-product.write()
+        version = items[0].__strip__()
+        date_str = items[1].__strip__()
+        if endoflife.DEFAULT_VERSION_PATTERN.match(version) and DATE_PATTERN.match(date_str):
+            date = dates.parse_date(date_str)
+            product_data.declare_version(version, date)