Adds an ability to use preallocated memory instead of file

[erhoof]

Speeds up execution on low-powered devices via USE_ALLOCATED_SPACE define

Also i added some c-style casts, to make possible compiling via C++ compiler

[paulmenzel]

Thank you for your contribution. Two minor comments. It’d be great if you added benchmark data to the commit message. Second, it’d be great if you used imperative mood in the commit message summary/title.

[Voidless7125]

You have a RAM leak. Here's the fix:

    if (!emu_memory)
    {
        fclose(f); // Fix
        return -1;
    }

I checked with Cppcheck. (And tested and confirmed)