Move threading calls into a basic user space library.

lib/mammoth/include/mammoth/debug.h

@@ -0,0 +1,3 @@
+#pragma once
+
+void dbgln(const char*);

lib/mammoth/include/mammoth/thread.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <stdint.h>
+
+class Thread {
+ public:
+  typedef void (*Entry)(void*);
+
+  Thread(Entry e, const void* arg1);
+
+ private:
+  uint64_t thread_cap_;
+};