Add RU locale

[senpos]

Closes #227

locale.py generated with clock on Windows 10.
Tests are included.

Tested by me on Windows 10 with Python 3.6.4.

Thanks to @creazero for testing on Kubuntu 17.10 with Python 2.7 and 3.6.3.

Seems to be working fine. If you encounter any problems - feel free to update related issue or this PR.

[senpos]

Due to the Changelog:

diff_for_humans() now returns a few seconds where appropriate.

Is it now required for translations as well?

As I can see, not all current translations use this feature, but it is quite easy to implement with:

translations = {
    ...
    'units': {
        'few_second': 'a few seconds'
    },
    ...

Am I right?

[senpos]

@sdispater

Hello.

Do I have to change something here, so you could merge it?

The only failing thing is codecov, but it seems like there is nothing related to my changes.

[snurbol]

@sdispater
I agree, why you could not merge it?
Failed only coverage, and tests are same as yours.

[andreynovikov]

Any chance of it to be merged? @sdispater why are you asking for locale contribution and then do not accept them for almost a year?

[sdispater]

Thanks! And sorry for the delay