Mimesis: Add important data generators for RussiaSpecProvider

[lk-geimfari]

It would be awesome to add support for generating the following:

• [x] ИНН - Read more on wiki.
• [x] ОГРН - Read more on wiki.
• [x] КПП - Read more on wiki.
• [x] СНИЛС - Read more on wiki.
• [x] БИК - Read more on wiki.

[fried-sausage]

Adding Russian Address Classifier aka КЛАДР, or may be more recent and officially enforced: https://ru.wikipedia.org/wiki/ФИАС could also be useful

[lk-geimfari]

@fried-sausage Sure! I have updated list.

[fried-sausage]

@lk-geimfari thanks! Btw, if im not mistaken, the only method to generate random numeric string using mask is pin method in Code provider. I use it, but not for generating pin codes.
May be it could make sense to add such generic ("Provider-agnostic") methods to BaseProvider or make some generic provider and add such methods to it?

[lk-geimfari]

@fried-sausage Already! Function utils.custom_code which also used by Code.pin.