setup grab_buffer class for posix thread (WiP)
new file: grab_buffer_posixThread.h: grab_buffer class.
modified: main.cpp: add grab_buffer call (error: without object as git 5567de...).
setup grabuffer (compile and run well)
modified: main.cpp: setup object.
setup same object way for save buffer.
modified: main.cpp: call with object.
modified: save_posixThread.h: fail to remove static.
rename save buffer class.
modified: grab_buffer_posixThread.h: change related to save buffer class renaming.
modified: main.cpp: change related to save buffer class renaming.
renamed:  save_posixThread.h -> ../save_buffer_posixThread.h: rename posixThread_save_data and posixThread_save to posixThread_data_saveBuffer and save_buffer_posixThread
rename state mutex.
modified: grab_buffer_posixThread.h: add todo.
modified: main.cpp: change related to state mutex renaming.
modified: posixThread.h: rename state mutex for code clarity.
modified: save_buffer_posixThread.h: change related to state mutex renaming.
small changes
modified: grab_buffer_posixThread.h
modified: save_buffer_posixThread.h
clean mutex code.
modified: main.cpp: clean mutex code.
move grab buffer code lines from main to grab buffer class.
modified: grab_buffer_posixThread.h: add image buffer and current grabbed frame to class (from main).
modified: main.cpp: remove a few grab buffer code lines to integrate in grab buffer class; call new these functions.
move save thread object array to grab class.
modified: grab_buffer_posixThread.h: add save_thread function to init structure and create threads.
modified: main.cpp: remove corresponding code.
move save threads in grab buffer from main.
modified: grab_buffer_posixThread.h: add from main code related to save threads: start_save_thread and wait_save_thread functions.
modified: main.cpp: related changes.
setup single grab thread (i.e. no save thread, still need image naming in grab buffer)
modified: grab_buffer_posixThread.h: setup single grab thread (i.e. no save thread).
modified: main.cpp: clean code.
modified: save_buffer_posixThread.h: clean code.