Codechange: Template input buffer type in audio mixer. (#11505)

This reduces code duplication.

Codechange: automatic adding of _t to (u)int types, and WChar to char32_t

for i in `find src -type f|grep -v 3rdparty/fmt|grep -v 3rdparty/catch2|grep -v 3rdparty/opengl|grep -v stdafx.h`; do sed 's/uint16& /uint16 \&/g;s/int8\([ >*),;[]\)/int8_t\1/g;s/int16\([ >*),;[]\)/int16_t\1/g;s/int32\([ >*),;[]\)/int32_t\1/g;s/int64\([ >*),;[]\)/int64_t\1/g;s/ uint32(/ uint32_t(/g;s/_uint8_t/_uint8/;s/Uint8_t/Uint8/;s/ft_int64_t/ft_int64/g;s/uint64$/uint64_t/;s/WChar/char32_t/g;s/char32_t char32_t/char32_t WChar/' -i $i; done

Codechange: Remove duplicated includes. (#10888)

These are now included by stdafx.h so don't need to be included again.

Fix: Allow full sample range for 16-bit audio.

Clamping each sample value to half the available range could cause
unnecessary premature clipping with lots of sounds playing. This change
does not affect the actual volume level.

Fix: Apply master effect volume during mixing instead of sound start. (#8945)

This makes the volume control work as most players would expect, affecting
existing playing sounds as well as new sounds.

Feature: Framerate display window (#6822)

Frame rate and various game loop/graphics timing measurements and graphs. Accessible via the Help menu, and can print some stats in the console via the fps command.