Pytest-jsonschema

Bugfix

- Add MANIFEST.in file [ericof] [5](https://github.com/collective/pytest-jsonschema/issue/5)


Documentation

- Improve README.md with usage information [ericof] [4](https://github.com/collective/pytest-jsonschema/issue/4)

Feature

- Implement fixture to validate a file against a json schema [ericof] [1](https://github.com/collective/pytest-jsonschema/issue/1)
- Implement fixture to validate a string against a json schema [ericof] [2](https://github.com/collective/pytest-jsonschema/issue/2)
- Implement fixture to validate a data structure against a json schema [ericof] [3](https://github.com/collective/pytest-jsonschema/issue/3)