add flake8 in build check, reorder imports

[kelvintaywl]

This PR updates the SDK such that:

1. introduce flake8 as part of Travis CI build to ensure that we follow PEP8 guidelines as close as possible.
2. reordering of imports to follow import guidelines from PEP8 (ref: https://www.python.org/dev/peps/pep-0008/#imports).

I have explicitly set flake8 config to ignore max line length (defaults at 79 chars) though. perhaps we want to enforce a specific max line length?

[ardydedase]

Hi @kelvintaywl,

Let's stick to the standard 79 characters.
Also, the build has failed. Could it be because it failed the flake8 check?

Thanks for this!

Regards,
Ardy

[coveralls]

Coverage decreased (-0.9%) to 92.308% when pulling b446dee on kelvintaywl:add-flake8-reorder-imports into 0dd7eec on Skyscanner:master.

[kelvintaywl]

Hi @ardydedase

Thanks for the response!
I have set it to follow the recommended 79 char limitation then.
As a result, I have also formatted the codes to fit the 79-char limitation.

A small note, however, as I have elected to ignore the E402 rule from PEP8 as there seem to be a conflict between flake8's handling of checking E402 against dunder names such as __author__, __version__, etc.

build is currently failing as flake8 does not support python 2.6. I'm not sure if there's a strong motivation to support python 2.6 though.

[ardydedase]

Hi @kelvintaywl,

The changes are looking good. Noted the E402 rule as well.
I'm now considering ditching Python 2.6. It also causes us syntax problems sometimes.
Thanks a lot for your contribution!

Regards,
Ardy