Rearrange article id parsing to be more reliable

The article ID parser looks for a string at the end of a URL path with
a bunch of hex digits. But it also has to handle user, tag, and search
URLs.

* /@ba5eba11
* /tag/0ddba11
* /search?q=ba5eba11

Some URLs are encoded as params. The parser used to look at the result
of the path first, then the params. But paths that ended in
`global-identity-2` messed that up because `2` is a hex digit at the
end of the path. This changes the logic to parse params first and paths
second which gets around this.

spec/classes/article_id_parser_spec.cr

@@ -78,6 +78,14 @@ describe ArticleIdParser do
     result.should eq(Monads::Just.new("888888abcdef"))
   end
 
+  it "parses the post id for global identity 2 redirects" do
+    request = resource_request("/m/global-identity-2?redirectUrl=https%3A%2F%2Fexample.com%2Fmy-post-999999abcdef")
+
+    result = ArticleIdParser.parse(request)
+
+    result.should eq(Monads::Just.new("999999abcdef"))
+  end
+
   it "returns Nothing if path is a username" do
     request = resource_request("/@ba5eba11")