cleanups and fixes:
- refactor away metadata into just modelica and examples.toml
- refactor to use HashSet instead of Vec<String>
- proper error handling types/story
- validate incomplete identifiers (?)


- finish rebalance/resolve/rephrase for {x}
- latex output
- tangle demo
- http://blog.littleredcomputer.net/math/odex/js/2016/04/03/lotka-volterra.html

- show a variable table
- Van der Pol oscillator

- minimum viable library and daemon/API for accessing db of models
    => cross-model type validation
    => versioning/tagging allowing editing of dep tree
    => versioned transpiling
    => federation/merging
- minimum viable wiki-editor web front end on top of API

later:
- look at libsyntax for (maybe) rust idiomatic ways to do AST stuff
- more complete modelica support ("import" large files into multiple linked models)
- LICENSE (AGPL, CC0 for generated code)
- error pretty printer isn't great
- refactor Debug and Display for AST
- basic travis setup
- logging (slog? or default to 'INFO')
- testing framework with "raises" and "assert_gt"
- rename to "modell-dinge"?
- basic generation of python/julia code from model
- elm explorer?