Rewrite the entire code-base

The following changes are focused upon:
- Modularity
- Doing away with globals
- No heap allocations
- Better command line interface
- Switch from Xlib to XCB
- More verbose type definitions
- Implement a single-file config by utilising X-macros

include/signal-handler.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <bits/types/sigset_t.h>
+
+#include "timer.h"
+
+typedef sigset_t signal_set;
+typedef int (*signal_refresh_callback)(void);
+typedef int (*signal_timer_callback)(timer* const timer);
+
+typedef struct {
+    int fd;
+    const signal_refresh_callback refresh_callback;
+    const signal_timer_callback timer_callback;
+} signal_handler;
+
+signal_handler signal_handler_new(
+    const signal_refresh_callback refresh_callback,
+    const signal_timer_callback timer_callback);
+int signal_handler_init(signal_handler* const handler);
+int signal_handler_deinit(signal_handler* const handler);
+int signal_handler_process(signal_handler* const handler, timer* const timer);