Fixing backward compatibility with python2 and dependabot alerts

• Fixed open() function in setup.py that broke on python 2.7.3 because of encoding keyword argument. The fix calls io native library that ensures backward compatibility for the open() built-in function.
• Removed useless requirements.txt that caused the dependency bot to raise security alerts (because of some known vulnerabilities on django 3.0.X)

Continuous Integration

The current version implements the whole CI pipeline using Travis CI. Here is what the pipeline does:

1. Checks code formatting using black
2. Checks code validation using flake8
3. Runs unit-tests (with pytest)
4. Checks tests coverage using codecov

Also, more project details were displayed as badge in the project's main README file.

Community-related improvements: Detailed documentation, license, package config and some bugs fixs

• Documented the whole project in the README.md file.
• Fixed bug that raised ValueError instead of SerializationError during serialization.
• Made ValidationError available from django_rest.deserializers.
• Improved setup.py and updated project's version.
• Added MIT license file to the project (LICENSE.md).
• Added setup.cfg file.

Major bugs fixs

• Renamed PerforatedDeserializer into AllPassDeserializer.
• Refactored class-based decorated view for better performances.
• Fixed CSRF token bug for writing HTTP methods.
• Fixed Permission evaluation (made dynamic).

Introducing Deserializers, and improving core `@api_view` decorators

Main changes:

• Implementing the first Deserializerclass
• Assuring support for all python's versions (2.7+, 3+), and django's versions (1.11+).
• Type hinting to improve code's readability.

Core @api_view changes:

• Supporting deserializer_class parameter.
• Supporting deserializer class mapping (custom deserializers for each http method).
• Adding allow_forms parameter to accept forms data or raise error.
• Supporting for @api_view syntax (only @api_view() was supported before)
• Checking view's type to make sure it's either a function or a django.views.View class
• Normalizing requests payload between content_types, so that the output's always in the same format.
• Extracting query params and passing custom parameters for the view (query params, payload, url params, etc.).
• Decorating only class view's relevant methods (http methods) instead of all methods.
• Moving helpers function into separate file.