Python 3.5 support

[dzhu]

I would like to use sgqlc for a project that is currently committed to supporting Python 3.5 (among other versions). Would it be possible to add Python 3.5 support to sgqlc? I'm hoping it might not be a huge amount of work: I haven't done a thorough check, but I was able to install sgqlc, run sgqlc-codegen, and use the generated code to make some queries after very minimal changes to the code -- I just had to edit setup.py to change the version requirement and remove the one use of an f-string. It does look like getting the tests to run will be take a bit more tweaking, though.

[barbieri]

I never bothered to check, if the f-strings are the only issue, I'm fine to apply patches converting to more traditional string formatting.

[dzhu]

Thanks! But sorry, I'm not quite clear -- are you intending to work on this yourself or are you saying that PRs would be welcome?

[barbieri]

PRs would be welcome :-)

quite overloaded with work these days, not able to work on it myself.

[dzhu]

Sounds good. I'll take a look.