Virtual filesystem support

[BeastLe9enD]

Extended fast_obj_read_with_callbacks function to load from virtual file systems :)

[thisistherk]

Awesome - thanks! Few little nits:

• it needs a #include for size_t
• nullptr is a C++ thing, needs to compile with C too
• could you fix the unused parameter warnings in file_open etc (just change the user_data param to something like void* /*user_data*/ should do it I think)
• could you fix the indents in the new callbacks struct to match the rest of the code?

clang -Wall -Wextra fast_obj.c if your on Mac/Linux should point most of them out :)

[BeastLe9enD]

Ok, fixed it, also noticed that there is a warning with fopen on Windows which forces you to use Windows-specific fopen_s. Fixed it through _CRT_SECURE_NO_WARNINGS, hope thats ok !:)

[thisistherk]

Thanks! Couple of further tiny things, sorry! Think we should probably not define _CRT_SECURE_NO_WARNINGS. Generally I think we should write code to avoid warnings where possible, but we probably shouldn't actually turn warnings off - leave that up to the user :)

Also need to tweak the unused var stuff a tiny bit. The variable declarations need to go at the top to work with C89 - so like:

{
    FILE* f;
    (void)(user_data);

[BeastLe9enD]

its fine!:) Incidentally, did not know that the variables must first be declared in C89

[thisistherk]

Brilliant - thanks!