Add option to handle ctrl-C

It would be nice if `ConsoleReader.readline()` could handle ctrl-C by returning immediately and signaling this to the application (possibly by throwing an exception). This needs to be distingishable from EOF / ctrl-D (which returns `null`) and the user entering a blank line by simply pressing enter. Applications that handle multi-line input typically respond to ctrl-C by clearing the multi-line input state. For example, the user can enter a SQL query over multiple lines and press ctrl-C to abort and start typing a new query.