YS binary and pkg installation plan

[ingydotnet]

YAMLScript's ys CLI binary can currently be installed using:

• bash <(curl https://yamlscript.org/install)
• brew install yaml/yamlscript/ys
• make install-ys from this repo

I want to start publishing libaries and apps written in YS.
YS 0.1.88 added support for the use command auto-installing from places like github, maven, etc and plain urls (like raw gists).
It's not fully complete yet but getting there.

I want to host ys ware under the @pkgys org, and have a package manager called called ysp.
I imagine you can install ysp with ys --install ysp after installing ys.
There should be a pkgys/index repo for people to register their ys pkgs.

Currently if you install with bash <(curl https://yamlscript.org/install) you can run ys --upgrade later to get the latest version.
This should be made to work, no matter how ys was first installed.

The goal is to make YS bootstrapping painless, and upgrading later as well.

[ingydotnet]

re #207 @danielbayley @delonnewman