Initial external decorator for annotating explicit import names; Use file name as default module name in imports; Emit empty memory if there are no static segments; Update TLSF and examples accordingly

tests/compiler/main.optimized.wat

@@ -2,11 +2,22 @@
  (type $iii (func (param i32 i32) (result i32)))
  (type $v (func))
  (global $main/code (mut i32) (i32.const 0))
- (memory $0 1)
+ (global $~started (mut i32) (i32.const 0))
+ (memory $0 0)
  (export "main" (func $main/main))
  (export "memory" (memory $0))
  (func $main/main (; 0 ;) (type $iii) (param $0 i32) (param $1 i32) (result i32)
-  (call $start)
+  (if
+   (i32.eqz
+    (get_global $~started)
+   )
+   (block
+    (call $start)
+    (set_global $~started
+     (i32.const 1)
+    )
+   )
+  )
   (get_global $main/code)
  )
  (func $start (; 1 ;) (type $v)