Move source files to src/, add Makefile, fix all build and linkage errors, etc.

exosphere/src/timers.c

@@ -0,0 +1,8 @@
+#include "timers.h"
+
+void wait(uint32_t microseconds) {
+    uint32_t old_time = TIMERUS_CNTR_1US_0;
+    while (TIMERUS_CNTR_1US_0 - old_time <= microseconds) {
+        /* Spin-lock. */
+    }
+}