Callee cleans the stack and first two arguments are passed in registers ecx and edx.
You could emulate this by choosing stdcall and setting the custom_registers on the arguments manually, but this is easier.
A "Functions" section is parsed in gamedata files that allow you to define the signature of functions including metadata like the calling convention and specifying the register an argument is passed in.
A new native DHookCreateFromConf can be used to setup a hook or detour from one of that function sections in the "Functions" section.
If the compiler decided to pass an argument in a register on an internal function instead of pushing it on the stack to save time, allow us to specify the register the parameter is going to be in.
DHookAddParam received another parameter to set the register.
