UI: Add a link to the GitHub commit in the Help menu

The "Go to GitHub commit" item in the Help menu opens the URL
https://github.com/solvespace/solvespace/commits/5efc148
and allows the user to see the date of the commit that SolveSpace was
built from.

Closes solvespace#1172

src/config.h.in

@@ -2,6 +2,7 @@
 #define SOLVESPACE_CONFIG_H
 
 #define PACKAGE_VERSION "@PROJECT_VERSION@~@solvespace_GIT_HASH@"
+#define GIT_HASH_URL "https://github.com/solvespace/solvespace/commits/@solvespace_GIT_HASH@"
 
 /* Non-OS X *nix only */
 #define UNIX_DATADIR "@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_DATAROOTDIR@/solvespace"

src/graphicswin.cpp

@@ -183,6 +183,7 @@ const MenuEntry Menu[] = {
 { 0, N_("&Help"),                       Command::NONE,             0,       KN, mHelp  },
 { 1, N_("&Language"),                   Command::LOCALE,           0,       KN, mHelp  },
 { 1, N_("&Website / Manual"),           Command::WEBSITE,          0,       KN, mHelp  },
+{ 1, N_("&Go to GitHub commit"),        Command::GIHUB,            0,       KN, mHelp  },
 #ifndef __APPLE__
 { 1, N_("&About"),                      Command::ABOUT,            0,       KN, mHelp  },
 #endif

src/solvespace.cpp

@@ -1056,6 +1056,10 @@ void SolveSpaceUI::MenuHelp(Command id) {
 PACKAGE_VERSION, 2022);
             break;
 
+        case Command::GIHUB:
+            Platform::OpenInBrowser(GIT_HASH_URL);
+            break;
+
         default: ssassert(false, "Unexpected menu ID");
     }
 }

src/ui.h

@@ -172,6 +172,7 @@ enum class Command : uint32_t {
     // Help
     LOCALE,
     WEBSITE,
+    GIHUB,
     ABOUT,
 };