📜 Add better documentation across the compiler. (#3)

These changes pay particular attention to API endpoints, to try to
ensure that any rustdocs generated are detailed and sensible. A good
next step, eventually, might be to include doctest examples, as well.
For the moment, it's not clear that they would provide a lot of value,
though.

In addition, this does a couple refactors to simplify the code base in
ways that make things clearer or, at least, briefer.

Cargo.toml

@@ -19,7 +19,7 @@ cranelift-module = "0.94.0"
 cranelift-native = "0.94.0"
 cranelift-object = "0.94.0"
 internment = { version = "0.7.0", default-features = false, features = ["arc"] }
-lalrpop-util = "^0.19.7"
+lalrpop-util = "^0.20.0"
 lazy_static = "^1.4.0"
 logos = "^0.12.0"
 pretty = { version = "^0.11.2", features = ["termcolor"] }
@@ -30,4 +30,4 @@ tempfile = "^3.5.0"
 thiserror = "^1.0.30"
 
 [build-dependencies]
-lalrpop = "^0.19.7"
+lalrpop = "^0.20.0"