Add multiline input support to prompt

[vinc]

> print "this is an input that fits on one line"

> print "this is a very looooooooooooooooooooooooooooooooooooooooooooooooooooooo
ooooooooooooooooooooooooooooooooooong input that fits over two lines"

> print "this is an extremely looooooooooooooooooooooooooooooooooooooooooooooooo
oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
ooooooooooooooooooooooooooooooooooong input that fits over three lines"