Error on issue reference in doc requests

Issues can be referenced after @TarantoolBot doc request. Though it will
be parsed as a part of the documentation request which is wrong.

This patch makes the checkpatch issue an error if there is an issue
reference in the doc request body. Only the most popular constructions
are handled (e.g. "closes", "part of" etc.) to avoid false-positives.

Examples of handled errors:
```
@TarantoolBot document
Closes #234
Follow-up     #234
Follows-up: #234
EE-Issue #234
Close #999
Close #999, #123, #9900
Close http://github.com/reference/to_issue
Close tarantool/tarantool-ee#234
```

These aren't handled (referencing commits and uncommon constructions):
```
@TarantoolBot document
Follows up the commit 1e94aeff
Closes the issue #1234
Repairs #1234
```

Author: georgiy-belyanin

checkpatch.pl

@@ -500,6 +500,36 @@ sub hash_show_words {
 	NO_CHANGELOG
 )};
 
+our $github_ref = qr{(https?:\/\/)?(www\.)?github\.com\b([-a-zA-Z0-9()@:%_\+.~\#?&\/=]*)};
+our $github_issue_ref = qr{((tarantool\/\S+)?\#[1-9][0-9]*)};
+
+our $github_issue_markers = qr{(?x:
+	Close|
+	Closes|
+	Part\s+of|
+	Part-of|
+	Issue|
+	Follow\s+up|
+	Follows\s+up|
+	Follow-up|
+	Follows-up|
+	Needed\s+for|
+	Needed-for|
+	Fix|
+	Fixes|
+	Fixed|
+	See|
+	See\s+also|
+	See-also|
+	Related\s+to|
+	Related-to|
+	Related|
+	Relates|
+	Workaround|
+	Implement|
+	Implements
+)};
+
 sub edit_distance_min {
 	my (@arr) = @_;
 	my $len = scalar @arr;
@@ -2723,6 +2753,10 @@ sub process {
 				      "Please move $1 tag before doc request\n");
 			}
 		}
+		if ($in_commit_log && $has_doc && $line =~ /^($github_issue_markers)\s*:?\s*($github_issue_ref|$github_ref)/) {
+			ERROR("ISSUE_IN_DOC",
+			      "Please move \"$line\" issue reference before doc request\n");
+		}
 		if ($in_commit_log && $line =~ /^\@TarantoolBot document$/) {
 			$has_doc = 1;
 		}