Add simple bar that display on bottom of screen

No text display yet.
bar: Show always the last line retrieved from stdin
Makefile: Add bar to all target
bar: Check monitor id to be valid
bar: Use DOCK hint (for gnome)
bar: Fix strut bottom_start_x and end_x

The windows allocation.x is 0, although its displayed with offset,
seems its relative to window itself. So use monitor position instead.
bar: Incremental line display
Makefile: Add some used pkgconfig modules for bar
README: Add description for bar
bar: Remove unneeded default rule for GIOStatus
Merge branch 'bar'