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).

src/Bar.zig

@@ -7,6 +7,9 @@ const Bar = @This();
 /// Standard base DPI at a scale of 1
 const base_dpi = 96;
 
+/// Default strftime string to use for the clock
+pub const default_time_format = "%Y-%m-%d %H:%M, %A";
+
 context: *Context,
 
 /// The timezone of the computer.
@@ -61,6 +64,9 @@ pub const Options = struct {
     vertical_padding: u8 = 5,
     /// Horizontal padding between bar edges and content, in pixels
     horizontal_padding: u8 = 5,
+
+    /// strftime format string for the clock display
+    time_format: []const u8 = default_time_format,
 };
 
 pub fn init(context: *Context, output: *Output, options: Options) !Bar {
@@ -240,7 +246,7 @@ pub fn draw(bar: *Bar) !void {
     // Convert time to a string
     var time_buf: [255:0]u8 = undefined;
     var time_writer = Io.Writer.fixed(&time_buf);
-    try dt.strftime(&time_writer, "%H:%M");
+    try dt.strftime(&time_writer, options.time_format);
 
     // Convert date string to Unicode codepoints
     const time_codepoints = try utils.utf8ToCodepoints(time_writer.buffered());