Fix fill-paragraph in multiline string

[mlechu]

Fix #24, and fix our indent function moving a closing """ line. Feel free to close if this isn't the intended behaviour

[tpapp]

Thanks for doing this! It does fix most of the issue, however, if I call the fuction on Firstline in

"""
Firstline

Nullam eu ante vel est convallis dignissim. Fusce suscipit, wisi nec facilisis
facilisis, est dui fermentum leo, quis tempor ligula erat quis odio. Nunc porta
vulputate tellus. Nunc rutrum turpis sed pede. Sed bibendum. Aliquam posuere. Nunc
aliquet, augue nec adipiscing interdum, lacus tellus malesuada massa, quis varius mi
purus non odio. Pellentesque condimentum, magna ut suscipit hendrerit, ipsum augue
ornare nulla, non luctus diam neque sit amet urna. Curabitur vulputate vestibulum lorem.
Fusce sagittis, libero non molestie mollis, magna orci ultrices dolor, at vulputate
neque nulla lacinia eros. Sed id ligula quis est convallis tempor. Curabitur lacinia
pulvinar nibh. Nam a sapien.
"""

it ends up aligning it with the preceding """, can this be prevented?

Also, can you please add tests? See the examples in the file.

[tpapp]

Apparently the error above was a local glitch to my config, so this is fine as it is. Thanks!