Handle docstring in raw format in main source file

[smit-hinsu]

Tested with ./run_tests.sh

[smit-hinsu]

@davidstanke Please take a look.

[davidstanke]

Hey! I'm not comfortable merging this -- I'm not engaged on implementation of Bazel/Python features. So I'll pass to @brandjon, who is.

[smit-hinsu]

Thanks @davidstanke for adding Jon on the PR.

[brandjon]

I'm not familiar with subpar's implementation details, but the change looks simple enough, and Douglas already signed off on it.

[brandjon]

Hm, actually I don't appear to have merge rights in this repo. Not sure who does. I'll look into that...