Add time_format config for custom strftime strings

This lets the user change to any time format they want in the bar.
As part of this, we also change the bar to re-draw every second (to
allow using seconds in the time format string).

docs/CONFIGURATION.md

@@ -147,6 +147,7 @@ bar {
 | `position`           | enum   | `top`              | Bar position (`top` or `bottom`)              |
 | `vertical_padding`   | u8     | `5`                | Vertical padding above and below text         |
 | `horizontal_padding` | u8     | `5`                | Horizontal padding between bar edges and text |
+| `time_format`        | string | `%Y-%m-%d %H:%M, %A` | strftime format string for the clock display (an empty string hides the clock) |
 
 ### Margins
 

docs/TODO.md

@@ -10,7 +10,6 @@ These are in rough order of my priority, though no promises I do them in this or
 - [ ] Support configuring bar item positions (left/center/right)
 - [ ] Support overriding config location
 - [ ] Add support for center-primary layout
-- [ ] Support 12-hour clock format (maybe take any time format string?)
 - [ ] Support per-output bar visibility
 - [ ] Support more window rule options (e.g. ssd/csd)
 - [ ] Support solid `background-color` fallback (no wallpaper)
@@ -50,3 +49,4 @@ These are in rough order of my priority, though no promises I do them in this or
 - [x] Support configuring primary vs secondary stack side
 - [x] Add focused window title to bar
 - [x] Add bar padding to config
+- [x] Support 12-hour clock format (maybe take any time format string?)