Fix call site when using Pool.prototype.query

This fixes the call site for long stack traces when using the query
method on a pool object. Before the stack trace would only lead up
to inside the getConnection method instead of the library caller.
Merge pull request #715 from dougwilson/fix/pool-long-stack-trace

Fix call site when using Pool.prototype.query
add example of using pool directly
Merge pull request #739 from coderhaoxin/master

add example of using pool directly