docs: add to TODO file

Signed-off-by: Karel Zak <kzak@redhat.com>

Documentation/TODO

@@ -1,6 +1,17 @@
 
  Note that items with (!) have high priority.
 
+- add functions strtime_short(), strtime_iso(), strtime_ctime(), ...
+
+- cleanup lib/path.c:
+   - always return rc from all functions
+   - introduce control struct and use openat() from top-level path 
+     (e.g. top-level is /proc, etc)
+- use lib/path.c as low-level API for lib/sysfs.c
+   - now we duplicate code in functions like {path,sysfs}_read_u32, etc. 
+   - it would be also nice to have a way how to redirect sysfs.c functions 
+     to /sys snapshots (e.g. lsblk regression tests)
+	
 lsblk
 -----
   - currently it does not show mountpoint for all devices in btrfs RAID. It's because