Add JPG/PNG Screenshot with no stalls

[L3-M]

Create a new screenshot function that doesn’t freeze the game. Currently, taking a screenshot (F12 for BMP) causes a pause and can even crash in windowed mode. GenTool addressed this by adding a JPG/PNG screenshot on F11, which saves a compressed image without causing the game to stall.

Creating a bmp image with F12 will cause a crash in windowed mode when the window hits the border of the desktop.

[xezon]

I also noticed that the original F12 screenshot cannot be taken during the loading screen, which may be a key input issue.

[mrtnptrs]

GeneralsOnline implemented this feature (JPEG) in its last update in a threaded manner that should not hamper performance or result in stalls; perhaps its implementation could be borrowed from. See the following commits:

• GeneralsOnlineDevelopmentTeam@a18c2e5
• GeneralsOnlineDevelopmentTeam@a69dd6b

[xezon]

For GenTool I used the CxImage library to export (and modify) JPG and PNG images. It is simple to use.

https://www.codeproject.com/articles/CxImage