Added proper support for multi-function operations, segregating
the API in single-function and multi-function operations.
Removed resultset as I/O object, the read_xxx owning functions
and read_all.
Unit test infrastructure for async testing.
Reference types lifetime fixes.
Removed connection::valid.
Fixed a serialization bug for statements with no parameters.
Binary protocol strings now use the type recommended by MySQL.
Refactored Jamfile to match best practices.
Updated description in libraries.json.
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