Dispatch a thread to update terrain data on the fly

Currently I update the whole VBOs using glMapBuffer in the main
thread in every 500 frames for experiment, the dispatched thread
use the mapped pointers return by main thread to update VBO data.
During the update, no frame can be drawn, this should be solved in
the following commits by using multi buffers.

BTW:
1. some config has changed to confort my experiment, these changed
   config values should be placed in a specific file in the future.
2. remove some uneeded outputs
3. BUG: close the tiff img file (TIFFClose) after usage to prevent too
   many open files

Signed-off-by: plysan <plysab@gmail.com>