lib: move conf parsing to lib/conf.c and refactor to not rely on getcwd/chdir

This fixes https://github.com/voidlinux/xbps/issues/158

include/xbps.h.in

@@ -594,6 +594,12 @@ struct xbps_handle {
 	 * Full path to the xbps configuration directory.
 	 */
 	char confdir[XBPS_MAXPATH+sizeof(XBPS_SYSCONF_PATH)];
+	/**
+	 * @var confdir
+	 *
+	 * Full path to the xbps configuration directory.
+	 */
+	char sysconfdir[XBPS_MAXPATH+sizeof(XBPS_SYSDEFCONF_PATH)];
 	/**
 	 * @var rootdir
 	 *

include/xbps_api_impl.h

@@ -155,5 +155,6 @@ xbps_array_t HIDDEN xbps_get_pkg_fulldeptree(struct xbps_handle *,
 		const char *, bool);
 struct xbps_repo HIDDEN *xbps_regget_repo(struct xbps_handle *,
 		const char *);
+int HIDDEN xbps_conf_init(struct xbps_handle *);
 
 #endif /* !_XBPS_API_IMPL_H_ */