Connects to ros2/demos#185

I wonder why the implementation of FastBuffer::resize can't resize an empty buffer below 200.
https://github.com/eProsima/Fast-CDR/blob/master/src/cpp/FastBuffer.cpp#L45-L81

If I have an empty buffer and want to resize it to an exact number of size - let's say I know how much data I want to copy into it - the minimum size of it is BUFFER_START_LENGTH, which is hard set to 200
https://github.com/eProsima/Fast-CDR/blob/master/src/cpp/FastBuffer.cpp#L23

why is that?