Consider activation frame for stack height metering (#2)

* Charge a base cost for calling a function

* Added regression test for empty functions

* Satisfy clippy

tests/fixtures/stack-height/table.wat

@@ -1,15 +1,15 @@
 (module
   (import "env" "foo" (func $foo))
   (func (param i32)
-     get_local 0
-     i32.const 0
-     call $i32.add
-     drop
+    get_local 0
+    i32.const 0
+    call $i32.add
+    drop
   )
   (func $i32.add (export "i32.add") (param i32 i32) (result i32)
     get_local 0
-	get_local 1
-	i32.add
+	  get_local 1
+	  i32.add
   )
   (table 10 anyfunc)