Make some reorganization in struct xbps_handle.

The variables to set cachedir, rootdir and metadir have been
changed to "array of chars", this way there are no extra allocations.

Update clients accordingly and bump API version.

bin/xbps-query/main.c

@@ -193,8 +193,10 @@ main(int argc, char **argv)
 	/*
 	 * Initialize libxbps.
 	 */
-	xh.rootdir = rootdir;
-	xh.cachedir = cachedir;
+	if (rootdir)
+		strncpy(xh.rootdir, rootdir, sizeof(xh.rootdir));
+	if (cachedir)
+		strncpy(xh.cachedir, cachedir, sizeof(xh.cachedir));
 	xh.conffile = conffile;
 	xh.flags = flags;