Provide command-line interface

[qsantos]

Makes the following possible:

python -m swagger_spec_validator "http://petstore.swagger.io/v2/swagger.json"

[coveralls]

Coverage decreased (-2.9%) to 95.522% when pulling ebceb95 on qsantos:master into 2a99f42 on Yelp:master.

[sjaensch]

Thanks for your contribution! Please also check the output of the travis run and fix the issues pre-commit mentioned. You can run make install-hooks to make sure those hooks will be run when you commit code.

[sjaensch]

These requirements are already listed in setup.py, no need to add them here.

[qsantos]

Apparently, the correct way is to put a line with a single . so that pip install -r requirements-dev.txt will automatically look in setup.py as well. I've pushed a new version reflecting this.

[nicktimko]

See #105 which includes some basic tests, an entrypoint, documentation, and processing of the raised exception to print the message rather than dumping a traceback.