[fine] Gobs of work

- Assertion improvements
- Type check function calls
- Functions in the environment
- Compile function calls

fine/tests/expression/errors/no_arg_pollution.fine

@@ -0,0 +1,6 @@
+fun foo(x: f64) {}
+x;
+
+// @type-error: 19 cannot find value x here
+// Used to have a bug where statements after a function declaration would
+// bind to the declaration's arguments, whoops.