Substantially refactor ~everything to separate concerns and improve flow clarity

Highlights:
- Remove all use of malloc and friends
- Refactor message handling functions to work with references
- Move core message read => triage => respond logic loop to main
  function
- Improve message triage and support follow-up messages
- Refactor hex byte parsing
- Disable periodic interrupt when not playing

src/queue.c

@@ -0,0 +1,58 @@
+#include <stddef.h>
+#include <stdint.h>
+
+#include "avclandrv.h"
+#include "queue.h"
+
+void constructQueue(Queue_t *q, void *buf, uint8_t size, uint8_t len,
+                    uint8_t constructFull) {
+  q->read = 0;
+  q->size = len;
+  if (!!constructFull) {
+    q->write = len;
+
+    for (uint8_t i = 0; i < len; ++i) {
+      q->buf[i] = buf;
+      buf = (char *)buf + size;
+    }
+  } else {
+    q->write = 0;
+  }
+}
+
+void constructEmptyQueue(Queue_t *q, uint8_t size, uint8_t len) {
+  constructQueue(q, NULL, size, len, 0);
+}
+
+uint8_t isEmpty(const Queue_t *q) { return (q->write == q->read); }
+
+static inline uint8_t isFull(const Queue_t *q) {
+  return ((q->write - q->read) == q->size);
+}
+
+static inline uint8_t qMask(const Queue_t *q, uint8_t pos) {
+  return pos & (q->size - 1);
+}
+
+uint8_t pushQueue(Queue_t *q, void *x) {
+  if (isFull(q))
+    return 1;
+
+  q->buf[qMask(q, q->write++)] = x;
+
+  return 0;
+}
+
+const void *peekQueue(const Queue_t *q) {
+  if (isEmpty(q))
+    return NULL;
+
+  return q->buf[qMask(q, q->read)];
+}
+
+void *popQueue(Queue_t *q) {
+  if (isEmpty(q))
+    return NULL;
+
+  return q->buf[qMask(q, q->read++)];
+}