* Location, error formatting and stack trace improvements
* Static context for AST nodes
* Thunks no longer need `name`
* Prototype for showing snippets in error messages (old format still
available)
* Use ast.Function to represent methods and local function sugar.
* Change tests so that the error output is pretty
* Improve imports
* Nonexistent file is now a runtime error (used to be ignored)
* Permission denied is a runtime error (used to be an internal error)
* Basic tests added for imports
* Renamed tests from .input to .jsonnet
* It's standard
* It's compatible with C++ test suite
* Editors enable syntax highlighting based on extension
* Importing .input looks weird
