Additional APIs for C++ StaticString

[ComicSansMS]

Brief feature description

Implement additional APIs on StaticString to bring it (roughly) to feature-parity with std::string.

Detailed information

The missing APIs are:

• missing append overloads
• insert
• erase
• replace
• resize
• find*
• starts_with
• ends_with
• contains
• substr
• add deduction guides where applicable

[FerdinandSpitzschnueffler]

Maybe also:

• clear
• operator+

[ComicSansMS]

Yes, clear is one I missed, thanks!

With operator+, the only way I can think of doing this is

template<uint64_t M>
StaticString<N+M> operator+(StaticString<M> const&);

i.e. the result string capacity would grow with each operation. I am unsure how useful this is in practice. I'm happy to hear people's opinions.