Added STS profile data structures plus serialize/deserialize helpers for storing profile state in a compact string form.

Registered the new STS source file in the Meson and Visual Studio build definitions.

src/common/meson.build

@@ -18,6 +18,7 @@ common_sources = [
   'scram.c',
   'server.c',
   'servlist.c',
+  'sts.c',
 	'text.c',
   'tree.c',
   'url.c',