Added validator btc addresses on format P2PKH

[ghost]

Hello. Please tell me what I did wrong?
Why doesn't travic-ci check?

[kvesteri]

@daveusa31 There are flake8 and isort errors. You can see the errors in the travis report.

[ghost]

I'm sorry, but I couldn't figure it out :(

[kvesteri]

You can check the errors locally by first installing flake8 and isort

>> pip install isort
>> pip install flake8 

The you can run the following command for isort:

>> isort --recursive --diff validators tests && isort --recursive --check-only validators tests

And for flake8

flake8 validators tests

[ghost]

Yeah, it works

[kvesteri]

Please add a doc block here defining how this function is to be used. See other functions of similar doc blocks. Also reference this doc block in the index.rst file

[ghost]

Added