String Theory 3.4

• Fix ST_WCHAR_LITERAL, ST_UTF16_LITERAL and ST_UTF32_LITERAL macros, which would previously create an incorrectly-sized buffer for non-empty strings.
• Add ST::buffer<T>::clear() and ST::string::clear() methods
• Deprecate ST::null and ST::null_t in favor of better alternatives:
  • Construction: Use {} or an explicit constructor (ST::string(), ST::char_buffer())
  • Comparison: Use .empty()
  • Assignment: Use .clear() or assign a default-constructed object.