Feature: Add Python import API usage

[MattTheCuber]

Before You Begin

Before proceeding, please make sure to follow these steps:

• I have checked for similar feature requests in the project's issue tracker
  to avoid duplicates.
• I have searched existing issues to see if this feature has been discussed
  before.

Feature Details

I would be great if we could use this tool dynamically in Python using imports to check licenses.

Describe the solution you'd like

Something like this:

import licensecheck

licensecheck.check()
licensecheck.check("/path/to/requirements.txt")

Describe alternatives you've considered

We could use system calls from Python.

[FredHappyface]

Hey thanks for the issue. I agree this would be awesome. I'll look at this next time I get some time on the project (in addition to some of the bugs too!)