Added source files initialization.

Now source files handling is delegated to functions defined
in `sourcefs.c` file. By encapsulating methods for managing
the underlying source files structure we ensure that all
code changes to the source file protection strategy will be
localized to `sourcefs.c` file.

Also changed Makefile to use more sane way of handling
options and build flags.

sources/sourcefs.c

@@ -0,0 +1,21 @@
+#define _GNU_SOURCE
+
+#include "sourcefs.h"
+
+#include <fcntl.h>
+
+static struct source_files_handle {
+  int root_fd;
+} handle;
+
+int source_init(const char *root_path) {
+  int root_fd = open(root_path, O_PATH);
+
+  if (root_fd == -1) {
+    return -1;
+  }
+
+  handle.root_fd = root_fd;
+
+  return 0;
+}