Front-end: Compute liveness to emit all `region_live_at` facts

[lqd]

In #48 a front-end was added to help start having unit tests, outside of rustc, as described in issue #26.

The region_live_at support is incomplete at the moment, as described in #45 (comment).

To compute liveness and emit those facts automatically, we'd need:

1. to extend the format and parser to accept def effects, here in the "IR" and here in the LALRPOP grammar.
2. do the computation, potentially with datafrog as described in this follow-up comment, and emit those facts in the parse_from_program function here.

Note that this computation can potentially be shared with rustc as well: in rust-lang/rust#51003.