REORG: include: move base64.h, errors.h and hash.h from common to to haproxy/

These ones do not depend on any other file. One used to include
haproxy/api.h but that was solely for stddef.h.
diff --git a/src/stats.c b/src/stats.c
index 8cb1840..0887925 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -36,7 +36,7 @@
 #include <common/time.h>
 #include <common/uri_auth.h>
 #include <haproxy/version.h>
-#include <common/base64.h>
+#include <haproxy/base64.h>
 
 #include <types/applet.h>
 #include <types/cli.h>