Add basic Russian support

[Forst]

This commit adds basic Russian support to DateTimeDifference.

However, fixes are required. The compound items are supposed to be different for "past" and "future" dates. For now they're translated as "past". Also, the "future" prefix (from_now) goes before the text:

second:
  past: "%count% секунда назад|%count% секунды назад|%count% секунд назад"
  future: "через %count% секунду|через %count% секунды|через %count% секунд"

The translation format is taken from Symfony/Component/Translation/PluralizationRules.php and has to be tested.

[norberttech]

@Forst thanks! Could you also please add one test before I merge that? Just like here: https://github.com/coduo/php-humanizer/blob/master/spec/Coduo/PHPHumanizer/DateTimeSpec.php#L175

[Forst]

@norzechowich Added a unit test for precise DateTime humanization according to how other languages were done. However, like other languages, "month/months" and "week/weeks" were not tested. Should I add such test cases as well?

[norberttech]

@Forst yes please, if this is not a problem for you of course.
Please also check why tests are failing.

[Forst]

@norzechovicz Will do. One thing is not entirely clear for me: will 35 days difference convert to "5 weeks" or "1 month 5/6 days"?

Also, should I add a test for separate items (i.e. not precise)?

The tests are failing because, as I said, from_now is a prefix in Russian, not a suffix. I can try to add support for prefixes, but it'll break existing translation pull requests.

[norberttech]

Ah right, prefix. Mmm sounds quite similar to #26 do you think its the same problem?

[Forst]

#26 has exactly the same problem. I suggest we introduce past_prefix and past_suffix, same for from_now.

[orestes]

I agree with @Forst. Introducing past_prefix, past_suffix, future_prefix and future_suffix would allow for more flexible translations.

[Forst]

I think it's possible to go further. Ideally, there should be no need to translate seconds, hours, months and so on twice: once for simple and once for precise dates. Instead, there should be common translations for both cases:

units:
    seconds: 'second|seconds'
    minutes: 'minute|minutes'
    ## snip ##
    years: 'year|years'

special:
    now_past: 'just now'
    now_future: 'just now'

prefixes:
    past: ''
    future: ''

suffixes:
    past: 'ago'
    future: 'from now'

[norberttech]

@Forst that make sense, could you prepare a PR for that?

[Forst]

@norzechowicz Will try to, I might need some help later on though. I'm closing this PR, will include Russian in the new request.

[norberttech]

@Forst thanks! Contact me if you would need any help.

[sam002]

@Forst Hi! Please check my changes for prefix support: #41
It as your design?