Create multithreaded Hello World example

[cztomczak]

Running multithreaded message loop gives best performance on Windows. Multithreaded message loop can be enabled only on Windows and Linux.

Related:

• Issue [Windows] Crash on exit with multi_threaded_message_loop=True #380 ("Crash on exit with multi_threaded_message_loop=True")
• PR Fixes issue #380[Windows] Crash on exit with multi_threaded_message_l… #412
• Issue Linux: Support for multi-threaded message loop mode #480 ("Linux: Support for multi-threaded message loop mode")

[jakogut]

CEF also introduced support for multi_threaded_message_loop on Linux recently.