*: improve multiple things e.g. making some strings.cc functions modify strings in-place, improving m4_ax_have_qt.m4 code, making anime_db.cc rely on std::optional rather than std::shared_ptr (which was stupid anyway)

includepaths
{
"../src"
}

files
{
("../src")
pugiconfig.hpp
pugixml.cpp
pugixml.hpp
}