Split secrets.h to public and core + miscellaneous cleanup

Also, changed some function names to this_style from thisStyle. More of
this in later commits.

server/core/maxscale/secrets.h

@@ -0,0 +1,43 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+/**
+ * @file core/maxscale/secrets.h - MaxScale config file password encryption/decryption
+ */
+
+#include <maxscale/secrets.h>
+
+MXS_BEGIN_DECLS
+
+#define MAXSCALE_KEYLEN 32
+#define MAXSCALE_IV_LEN 16
+
+/**
+ * The key structure held in the secrets file
+ */
+typedef struct maxkeys
+{
+    unsigned char enckey[MAXSCALE_KEYLEN];
+    unsigned char initvector[MAXSCALE_IV_LEN];
+} MAXKEYS;
+
+enum
+{
+    MXS_PASSWORD_MAXLEN = 79
+};
+
+int  secrets_write_keys(const char *directory);
+char *encrypt_password(const char*, const char *);
+
+MXS_END_DECLS