Replace contents of itoa() with snprintf()

[andy5995]

I wanted to ask if you want a change like this? I know it needs more work though, but I wanted to check with you before continuing.

[KaruroChori]

It cannot accept it because:

• https://cplusplus.com/reference/cstdlib/itoa/ while explicitly stating this function is not standard, shows a signature returning the out buffer. I would like to keep it consistent with that source of documentation.
• Base is not supported.
• I am considering https://github.com/fmtlib/fmt to replace all pritntf and C++ fmt as it would appear to be significantly faster.

Still, I am very positive about moving the implementation out of tcc into the main compiled application

• to make scripts faster & lighter
• because that code would be much better optimized by clang

Aside from that, at some point there should be some discussion on which features to expose to the C scripts beyond the specific functions/macros defined by vs. That fragment of libc is for the most part just a placeholder to have something functional, but we can decide to have a different runtime.

[andy5995]

@KaruroChori It's my understanding that the base wouldn't be needed if using snprintf().

As for the other things, I'm happy to close this. :)