use serde and semver instead of hand-written logic

[dherman]

Path to eliminating the hand-written logic for version data structures and for serialization of various data structures:

• config should use serde (with an IR if necessary)
• config should match the structure of RFC1 — just one hook for now
• catalog should store versions as an ordered, sorted collection
• catalog should support a resolve method that finds an available version that matches a spec
• move most Tool logic to Node, for now tailored to specifically being the Node launcher
• create a new top level Node launcher separate from launchbin/launchscript
• rename notion/main.rs to notion/notion.rs
• Node::new() should call session.node(&mut self) and get back the Version, instead of session.node_version()
• session.node() should check for project and if so get a VersionReq, otherwise use the current catalog Version
• when session.node() gets a VersionReq, try to find one already in catalog and return that
• when session.node() gets a VersionReq and there’s none in catalog, either use resolution plugin or default resolution logic
• config should have an IR for serialization
• default resolution logic should consult https://nodejs.org/dist/index.json but for now can hard-code a few versions
• plugin resolution logic should call the executable
• manifest should parse using serde
• manifest should just return the VersionReq
• remove the logic of installing from Manifest
• kill the lockfile module entirely
• kill the untoml module entirely
• kill the version module entirely
• session.install_node() should ask the catalog to do the fetching if it has a VersionReq
• catalog should initiate the plugin’s resolution protocol if it needs to resolve a VersionReq