Choose logging library.

[huntzhan]

Use easyloggingpp. Plan:

• replace all throw statement with proper logging string.
• replace iostream with easyloggingpp.

After closing this issue, keep working on #8 .

[huntzhan]

Building boost libraries would not be a problem(#54). Hence, use Boost.Log instead. Boost.Log is too heavy.

[huntzhan]

Introduce easyloggingpp would result in:

• linkage error of all testcases.
• much more time on compiling.

So, try to write a project specific logger instead.Currently just use std::cout for logging.