* move stuff to namespace util::xml
* scope down some enums
* split config load/save delegate types
* make config load take const so it can't mangle data
* an empty tag and a self-closing tag are semantically equivalent, so std::string can be used saving some manual allocation
* a valid tag can't have an empty name, so that can be std::string too
* still expose empty strings as nullptr to API users
* scope down the int_format enum
* # is not £ ffs
Use standard uint64_t, uint32_t, uint16_t or uint8_t instead of UINT64, UINT32, UINT16 or UINT8
also use standard int64_t, int32_t, int16_t or int8_t instead of INT64, INT32, INT16 or INT8
