Add Timer to wrap CPU clock_t and GPU cudaEvent_t based timing
Replace CPU timer with newly added Timer to benchmark net speed
Conflicts:

	tools/net_speed_benchmark.cpp
Add state machine, boost::posix_time based cpu timer & tests for Timer
Conflicts:

	tools/net_speed_benchmark.cpp
Fix the cpplint errors for benchmark Timer
Conflicts:

	tools/net_speed_benchmark.cpp