Extract can/ into its own crate, plus its deps

compiler/can/src/lib.rs

@@ -0,0 +1,14 @@
+pub mod annotation;
+pub mod constraint;
+pub mod def;
+pub mod env;
+pub mod expected;
+pub mod expr;
+pub mod module;
+pub mod num;
+pub mod operator;
+pub mod pattern;
+pub mod problem;
+pub mod procedure;
+pub mod scope;
+pub mod string;