Update assembly concepts to include export line

concept-code/eg1.vsm

@@ -1,3 +1,4 @@
+export @main {}
 @main = function() {
   call @f1 [1, 2, 3] %x
   apply @f2 %x [] %ignore

concept-code/eg1.vsxxd

@@ -1,16 +1,21 @@
-00: 0b04 0021 0d1c 0906 0106 0206 0300 0222
-10: 0d2c 0e02 0900 ff01 0e02 0000 0b07 0306
-20: 0e03 0e04 0504 0e02 0e05 0000 0b03 0002
-30: 0100
+00: 0d05 000a 000b 0400 210d 2300 0906 0106
+10: 0206 0300 0222 0d33 000e 0209 00ff 010e
+20: 0200 000b 0703 060e 030e 0405 040e 020e
+30: 0500 000b 0300 0201 00
 
 ---
 
-// Pointers occupy a single byte in this example because it is so small. The
-// length of the bytecode implicitly indicates the byte width needed for
+// Pointers currently occupy two bytes, restricting programs to 64kB.
+// In future, the length of the bytecode may indicate the byte width needed for
 // pointers (1, 2, 4, or 8, whichever is smallest and sufficient).
 
+    // export @main  {}
+00:           0d0500 0a00 // Default export is a pointer (0d) to 0500 (position
+                          // 5, little endian)
+                          // Named exports are an empty object (0a object, 00 end)
+
     // @main = function() {
-00:            0b  04  00 // function with 4 registers and 0 parameters
+05:            0b  04  00 // function with 4 registers and 0 parameters
                           //  0: %return
                           //  1: %this
                           //  2: %x
@@ -19,20 +24,20 @@
                           // the byte width for representing registers in this
                           // function
 
-    //   call @f1  [  1,   2,   3    ]  %x
-03:      21   0d1c 09 0601 0602 0603 00 02
+    //   call @f1    [  1,   2,   3    ]  %x
+08:      21   0d2300 09 0601 0602 0603 00 02
 
-    //   apply @f2  %x   [  ]  %ignore
-0f:      22    0d2c 0e02 09 00 ff
+    //   apply @f2    %x   [  ]  %ignore
+15:      22    0d3300 0e02 09 00 ff
 
     //   mov %x   %return
-17:      01  0e02 00
+1e:      01  0e02 00
 
     // }
-1b:    00
+22:    00
 
     // @f1 = function(%a, %b, %c) {
-1c:          0b  07  03 // function with 7 registers and 3 parameters
+23:          0b  07  03 // function with 7 registers and 3 parameters
                         //  0: %return
                         //  1: %this
                         //  2: %a
@@ -42,22 +47,22 @@
                         // ff: %ignore
 
     //   op* %b   %c   %_tmp0
-1f:      06  0e03 0e04 05
+26:      06  0e03 0e04 05
 
     //   op+ %a   %_tmp0 %return
-25:      04  0e02 0e05   00
+2c:      04  0e02 0e05   00
 
     // }
 2b:    00
 
     // @f2 = function() {
-2c:          0b  03  00 // function with 3 registers and 0 parameters
+33:          0b  03  00 // function with 3 registers and 0 parameters
                         //  0: %return
                         //  1: %this
                         // ff: %ignore
 
     //   op++ %this
-2f:      02   01
+36:      02   01
 
     // }
-31:    00
+38:    00

concept-code/eg2.vsm

@@ -1,3 +1,4 @@
+export @main {}
 @main = function() {
   mov 37 %x
   bind @foo [%x] %foo

concept-code/eg3.vsm

@@ -1,3 +1,4 @@
+export @main {}
 @main = function() {
   new @Counter [] %counter
   subcall %counter "inc" [] %ignore

concept-code/eg4.vsm

@@ -1,3 +1,4 @@
+export @main {}
 @main = function() {
   mov @Counter %Counter
   sub %Counter "prototype" %_tmp0

valuescript_compiler/src/assembler.rs

@@ -32,6 +32,9 @@ struct Assembler {
 
 impl Assembler {
   fn module(&mut self, module: &Module) {
+    self.value(&module.export_default);
+    self.object(&module.export_star);
+
     for definition in &module.definitions {
       self.definition(definition);
     }