Infrastructure

[jpn--]

This PR is an attempt to modernize this package and repository to current Python packaging standards and collaborative code practices. It does not address the fundamentals of the ActivitySim models directly.

Updates include:

• Testing via GitHub Actions instead of Travis
• Pre-commit hooks for code formatting
• Running as module (python -m activitysim)
• Flake8 style checks (?)
• pyproject.toml
• Versioning via git tags and setuptools_scm
• Publish interim docs to "develop" subdir on documentation site