Added specification for API.

requirements.txt

@@ -4,6 +4,8 @@ Flask-SQLAlchemy==2.4.1
 Flask-RESTful==0.3.8
 flask-marshmallow==0.11.0
 marshmallow-sqlalchemy==0.22.2
+apispec==3.3.0
+apispec-webframeworks==0.5.2
 mysqlclient==1.3.12
 redis==3.4.1
 mutagen==1.44.0