Implemented Intentionally slow expanding search

Implemented a slow expanding search.
You can delay each expansion by a command line option -d-%d.
The delay is implemented carefully to satisfy some requirements.

1. little memory(cache) requirement
The delay is implemented with little memory requirement (two integers).
It would cause little to no additional cache fault.

2. flat delay
The delay would applied evenly across each expansion.

3. no context switching
The delay is implemented in term of busy wait so that no context
switching would occur.