support for multiline strings, a-la-yaml or a-la-python

[odino]

from @omissis

What particularly do you think should be implemented? eg. this works but maybe you had something different in mind:

a = "
a
b
c
"

echo(a)

[omissis]

I was thinking about [something like this](yaml multiline string pipe) in terms of possibilities, but I guess the current solution works just as fine without block styling and chomping as it's allowed in yaml.