libpqxx 7.1.0: A whole new way of querying data

Another big update.

The bad news:

• Any string_traits<TYPE>::size_buffer() must now be noexcept.
• There's an extra data member in nullness: always_null. You'll need to implement to give your type full functionality.

The good news: there's a new way of retrieving data from the database! It's faster, it's easier, it includes conversion to a type of your choice. Using transaction::stream, you can query rows from the database straight into a std::tuple, and so, into local variables:

for (auto const [id, name] : tx.stream<int, std::string_view>("SELECT id, name FROM item"))
    process(id, name);

And in other news...

• stream_from now supports more or less arbitrary queries.
• Instead of a tuple of fields, you can pass stream_to a container as well.
• There is now to_buf support for string literals.
• Streaming data is now more efficient.
• The table name in stream_from is now escaped.
• You can now "convert" strings to std::string_view. Mind your lifetimes!
• A std::variant will now convert to string, if its member types do.
• If a stream_from row fails to convert, you can no longer retry it.
• from_string(field const &) now handles null values properly.
• Obsolete Windows build docs are gone.
• Added row::to(std::tuple<...>) — converts the whole row in one go.
• Unified the test suites. We no longer need test/unit/unit_runner.
• New helper: strip_t<...> to remove a type's constness and reference.
• Replace some custom templating in CMakeFiles with CMake globs.