improve multiline support

[Vosjedev]

Multiline command support is currently even worse than bash... In readline, if I go to a second line, it starts a prompt for the second line, on which I can't go back to the first line. Here, when I go to a second line, and I press arrow up, it just clears all lines and goes back to the previous command...

[armoar334]

A temporary fix for this has been implemented in commit 035605e706021481f5853a6873cbd175584794b0. I'll keep this issue open for now, as this isn't a great fix.