Support named pipes with SQL Server and MySQL

[pimeys]

On Windows platforms one can use the named pipes protocol instead of TCP to connect to the server. This protocol allows you to connect between different machines, or to the same machine, and is quite a lot faster compared to TCP. In some enterprise installations, TCP is not even allowed, meaning the only way to access the server is using named pipes.

This can be split into separate issues:

• Wait for named pipes support to land in Tokio (Design of named pipes support on windows tokio-rs/tokio#3511 + net: Provide a raw NamedPipe implementation and builders tokio-rs/tokio#3760)
• Wait for named pipes support then to land in mysql_async (the author of the Tokio PR is the author of mysql_async, so it'll come quite soon after the first PR is merged)
• Tiberius just works as-is. We need to change the connection string parsing a bit to allow usage of pipes instead of TCP.
• Document these changes.