secure stdio *printf_s, *scanf_s

[rurban]

This would be a lot of code to maintain, for just %n, the 2nd args for %s,%c,%] and the null pointer check for %s.

There are not many good small implementations. The best have license problems, like Huawei's securec.

• https://github.com/UVP-Tools/UVP-Tools/tree/master/uvp-monitor/secure
• freebsd, musl
• reactos, wine

[rurban]

Decided on => fmtlib #75

[rurban]

Changed my decision to https://github.com/mpaland/printf/
Work in branch printf

[rurban]

improved printf_s is in 3.7. sscanf_s not yet.