v0.3.0

• Major refactoring of core evaluation traits
  • The lowest-level "thing that can be evaluated" trait has changed from Shape (taking (x, y, z) inputs) to Function (taking an arbitrary number of variables).
  • Shape is now a wrapper around a F: Function instead of a trait.
  • Shape evaluators are now wrappers around E: BulkEvaluator or E: TracingEvaluator, which convert (x, y, z) arguments into list-of-variables arguments.
  • Using the VmShape or JitShape types should be mostly the same as before; changes are most noticeable if you're writing things that are generic across S: Shape.
• Major refactoring of how variables are handled
  • Removed VarNode; the canonical variable type is Var, which is its own unique index.
  • Removed named variables, to make Var trivially Copy + Clone.
  • Added vars() method to Function trait, allowing users to look up the mapping from variable to evaluation index. A Var now represents a persistent identity from Tree to Context to Function evaluation.
  • Move Var and VarMap into fidget::vars module, because they're no longer specific to a Context.
  • Op::Input now takes a u32 argument, instead of a u8
• Fixed a bug in the AArch64 JIT would which could corrupt certain registers during interval evaluation.