RoyaleAPI: Add top war clans endpoint

[gogaz]

Changes Description

Added top-level function to access /top/war endpoint from RoyaleAPI

Type of PR

• [ ] Bug Fix
• [x] Feature Addition

Checklist

• [x] Docstrings added (NumpyDoc)
• [ ] If necessary, add to the documentation files
• [x] Add to the CHANGELOG file
• [x] Tox checked

[gogaz]

Looks like there is a problem on the CI side, here's what I have when I run the tests locally :

========== test session starts ==========
platform win32 -- Python 3.5.4, pytest-4.4.1, py-1.8.0, pluggy-0.9.0
cachedir: .tox\py35\.pytest_cache
rootdir: C:\Code\clashroyale
collected 132 items

official_api\test_async.py .........................................                   [ 31%]
official_api\test_blocking.py .........................................                [ 62%]
royaleapi\test_async.py .........................                                      [ 81%]
royaleapi\test_blocking.py .........................                                   [100%]

========== 132 passed in 355.50 seconds ==========