We only need pip3 now on all OSes as cryptography now ships wheels on Linux 🎉.
Also remove `pip3 install --user` recommendation because that won't end up on $PATH.
- Addons now nest, which means that addons can manage addons. This has a number
of salutary effects - the scripts addon no longer has to poke into the global
addons list, we no longer have to replace/remove/boot-outof parent addons when
we load scripts, and this paves the way for making our top-level tools into
addons themselves.
- All addon calls are now wrapped in a safe execution environment where
exceptions are caught, and output to stdout/stderr are intercepted and turned
into logs.
- We no longer support script arguments in sys.argv - creating an option
properly is the only way to pass arguments. This means that all scripts are
always directly controllable from interctive tooling, and that arguments are
type-checked.
For now, I've disabled testing of the har dump example - it needs to be moved
to the new argument handling, and become a class addon. I'll address that in a
separate patch.
- Zap various occurrences of Python2 in docs and scripts
- Remove six from netlib, and some other places where obvious project-wide
search and replace works.
