Add the possibility of wrapping frame into a function

[neilccbrown]

What if when the user selects some code, we offer "d" for function definition as a possible wrapping action? It would move the code into a function in the functions section (bit confusing to move as we wrap, but in Strype-land the user will know functions have to be in the functions section). The main confusion is the user will need to fill in any parameters (as well as the name, obviously), but it feels like a nice natural way to do what JetBrains would call "Extract method".