Support for pool timeout

[trynn]

Please introducte a ConnectionTimeout to wait, when a connection is retrieved from the ConnectionPool. If no connection is available in-time, throw an exception (as is).

When ConnectionPool is active, please make

var conn = new FbConnection(ConnectionString);
await conn.OpenAsync();

to wait, until a free connection is available in the pool. Throwing an exception only after the timeout is expired.

also add blocking behaviour to

var conn = new FbConnection(ConnectionString);
conn.Open();

when no connection is available at the moment. Throwing an exception only after the timeout is expired.