add lots of TODOs for variables and type analysis of statements

- comp_ctx: replace Function.symbols to Function.env

examples/hello.ry

@@ -1,7 +1,9 @@
-// import std;
+const (
+    test_var = 1 + 3
+)
 
 fn f() i32 {
-    var a = 2;
+    var a = 3;
     return 2;
 }
 
@@ -9,10 +11,6 @@ fn f2() i32 {
     return f() + 2;
 }
 
-const (
-    piss = 1 + 3
-)
-
 enum B {
     a
     b