Update to asdf 0.8.0 plugin API

[jthegedus]

Is your feature request related to a problem? Please describe.

asdf 0.8.0 has support for documentation callbacks https://asdf-vm.com/#/plugins-create?id=optional-scripts

• bin/help.overview - This script should output a general description about the plugin and the tool being managed. No heading should be printed as asdf will print headings. Output may be free-form text but ideally only one short paragraph. This script must be present if you want asdf to provide help information for your plugin. All other help callback scripts are optional.
• bin/help.deps - This script should output the list of dependencies tailored to the operating system. One dependency per line.
• bin/help.config - This script should print any required or optional configuration that may be available for the plugin and tool. Any environment variables or other flags needed to install or compile the tool (for the users operating system when possible). Output can be free-form text.
• bin/help.links - This should be a list of links relevant to the plugin and tool (again, tailored to the current operating system when possible). One link per line. Lines may be in the format <title>: or just .

Describe the solution you'd like

Implement these scripts

Describe alternatives you've considered

Additional context

Might have to rethink existing solutions to deps etc.