Add possibility to provide data definitions

[Alexei-Kornienko]

This PR add possibility to provide data definitions to Swagger API.

I'm using schematics to describe models and I would like to publish their structure via Swagger specification.
For this I'm using a small library that I wrote and plan to publish it on PyPI - https://github.com/Alexei-Kornienko/schematics_to_swagger
Usage might look the following way:

setup_swagger(
    app,
    title='API',
    api_version="3.0.0",
    definitions=schematics_to_swagger.read_models_from_module(models)
)

[codecov-io]

Codecov Report

Merging #73 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master     #73   +/-   ##
======================================
  Coverage    88.7%   88.7%           
======================================
  Files           4       4           
  Lines         124     124           
======================================
  Hits          110     110           
  Misses         14      14

Impacted Files	Coverage Δ
aiohttp_swagger/helpers/builders.py	83.33% <ø> (ø)	⬆️
aiohttp_swagger/__init__.py	97.36% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 664b45e...d5f8fb9. Read the comment docs.