[Mammoth] Move most classes to the mmth namespace.

lib/mammoth/sync/semaphore.cpp

@@ -4,8 +4,12 @@
 
 #include "util/debug.h"
 
+namespace mmth {
+
 Semaphore::Semaphore() { check(ZSemaphoreCreate(&semaphore_cap_)); }
 Semaphore::~Semaphore() { check(ZCapRelease(semaphore_cap_)); }
 
 void Semaphore::Wait() { check(ZSemaphoreWait(semaphore_cap_)); }
 void Semaphore::Signal() { check(ZSemaphoreSignal(semaphore_cap_)); }
+
+}  // namespace mmth