Change examples to be doctests

Right now we use something like:

    def price_in_btc(self, minimum: float = 0, maximum: float = 2) -> str:
        """Generate random price in BTC.

        :param minimum: Minimum value of price
        :param maximum: Maximum value of price.
        :return: Price in BTC.

        :Example:
            0.5885238 BTC
        """

I suggest to change it to:

    def price_in_btc(self, minimum: float = 0, maximum: float = 2) -> str:
        """Generate random price in BTC.

        :param minimum: Minimum value of price
        :param maximum: Maximum value of price.
        :return: Price in BTC.

       >>> from mimesis import Business
       >>> provider  = Business()
       >>> provider.price_in_btc()
       0.5885238 BTC
        """

https://docs.python.org/3/library/doctest.html

But we need to freeze random here. So, it possible to use something like https://docs.pytest.org/en/latest/doctest.html#the-doctest-namespace-fixture

[valerievich]

Ok. Now I understand the whole idea of this issue. I am going to continue to work on this. It makes sense to create PR’s which consist of changes only for one provider I think. It would be easier to approve.

[lk-geimfari]

@ceccoemi We used to try to resolve this issue. I remember that this is problematic because of possible updates of files (JSON files where we store data for each provider).