Keep object locals only once in AST
For example this reduces the size of stdlib ast file
roughly 3x. Note that this change doesn't regenerate the stdlib,
so that the diff here is sane.
It is likely to slightly improve performance of code using
a lot of locals (~10% on bench.05.gen.jsonnet).
The desugaring is more strightforward now, and we're back
to desugaring each node exactly once.
* 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
* Array comprehensions
Implemented using flatMap.
The representation in AST was changed - now it expresses
the semantic structure better.
Ifs in comprehensions are not supported yet, but easy.
