Add support for 'context' keyword to translate()

[piotr-dobrogost]

translate() should support context keyword analogically to how it supports domain keyword.
Till then one can workaround this by wrapping string to translate in extra TranslationString like so:
translate(TranslationString(tstring, context='some_ctx'))

[ztane]

+1, and same applies of course to pluralization (Pluralizer) everywhere as well

[wichert]

translate() already has a context method ?

[ztane]

Wrong link, should be this but you're correct.

[ztane]

But docs are not up-to-date: http://docs.pylonsproject.org/projects/translationstring/en/latest/translation.html

[ztane]

And here http://docs.pylonsproject.org/projects/translationstring/en/latest/api.html#translationstring.Translator

[mmerickel]

Yes it looks like a few of the docstrings are out of date. A PR to fix these would be great.