Packaging improvements for v1.0.0

[goodmami]

This issue is just a collection of small tasks that can improve packaging (in a broad sense) for v1.0.0. The general goal is to simplify the project (fewer/simpler files relating to integrations) and use standard tools (already using TravisCI and ReadTheDocs... Maybe use codecov.io?).

• Pin several versions of documentation at ReadTheDocs: v0.9.2, v1.0.0
• Remove tox requirement
  • Better document virtual environment usage
  • Update .travis.tml
  • Remove tox.ini
• Fix PyPI readme
• Update badges
  • Only have 'develop' for TravisCI
  • Add Python version, PyPI package version (https://shields.io/)
  • Add code coverage (codecov.io or coverage-badge) Pass on this for now; the CONTRIBUTING.md file explains how to get test coverage
• Disable the defunct wiki
• Git annotated tags (see Look into git annotated tags for future releases #158) Also pass for now; there's no obvious need at this time
• Make delphin and delphin.codecs namespace packages (see Make delphin a namespace package #222; but distribute all together for now)
• Release v1.0.0 as delphin on PyPI (see Change delphin namespace to pydelphin? #182) Until there's a reason to separate a delphin base package from PyDelphin, there seems to be little need to upload to the delphin project on PyPI.