Automatically integrates git build information into executables.

Usage:
func.exe -V
adnl-pong -V
validator-engine -V
and so on.
Result will be shown in the following format:
Func build information: [ Commit: d8b751d7a5, Date: 2021-02-27 14:34:41 +0200]

git.h

@@ -0,0 +1,29 @@
+#pragma once
+#include <string>
+
+class GitMetadata {
+public:
+  // Is the metadata populated? We may not have metadata if
+  // there wasn't a .git directory (e.g. downloaded source
+  // code without revision history).
+  static bool Populated();
+
+  // Were there any uncommitted changes that won't be reflected
+  // in the CommitID?
+  static bool AnyUncommittedChanges();
+
+  // The commit author's name.
+  static std::string AuthorName();
+  // The commit author's email.
+  static std::string AuthorEmail();
+  // The commit SHA1.
+  static std::string CommitSHA1();
+  // The ISO8601 commit date.
+  static std::string CommitDate();
+  // The commit subject.
+  static std::string CommitSubject();
+  // The commit body.
+  static std::string CommitBody();
+  // The commit describe.
+  static std::string Describe();
+};