API to treat output results outside of robocop

Feature: It would be useful to implement an API that returns robocop output results.

For example:

from robocop.run import run_robocop

test = run_robocop()

In this specific scenario it would be very useful to retrieve the output in order to manage data outside of the robocop context (for example reports, badges and more).

[bhirsz]

Output looks great.

For returning the output I can create special method - I want to keep it separate, ie have current run() be described as run_cli() and for running from python run(). It would allow bit different configuration (easier) and we can return payload from run() while run_cli() would behave the same as it is now.

We also need to add unit tests, I can cover that.

[bhirsz]

Closed with #252