Configurable connect function

[ywangd]

The connect function does all the things that are required for connection itself. However there could be other things around it which could be customised, e.g. execute a command/script after a connection is created. This particular feature is implemented with a callback (#160). However there are variations which make it too much to implement, e.g. execute a command/script before a connection is created.

It is already possible to define a custom function that does what connect does and more. This new function can be used in place of connect function after the peek is launched. However, at launch time, the connect function is used internally to create the default connection and this is not replacable. Do we want to allow it to be replaced? Or is it sufficient if #162 is implemented?

[ywangd]

Accidentally closed. Reopen.