Finish up parser and assembler with more-or-less complete syntax

Major changes inlude:

* Bit the bullet and now instructions have their length hard-coded
* Move from_utf8 object parsing to be done by their objects (instead of
  a Parser god object)
* A list of AST sections are assembled into an Object using the new
  vm::obj::assemble module.
* Changed the object layout some in the spec, and adjusted code to match
  this.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/vm/inst.rs

@@ -2,13 +2,14 @@ macro_rules! instructions {
     {
         $($variant:ident = $value:expr),* $(,)?
     } => {
-        pub type InstOp = u16;
 
         $(
             pub const $variant: InstOp = $value;
         )*
     };
 }
+pub type InstOp = u16;
+
 
 instructions! {
     ADD        = 0x0000,
@@ -37,3 +38,37 @@ instructions! {
     HALT       = 0xF000,
     NOP        = 0xF001,
 }
+
+pub fn inst_len(op: InstOp) -> usize {
+    match op {
+        // 2 bytes
+        INEG
+        | INV
+        | NOT
+        | HALT
+        | NOP => 2,
+        // 4 bytes
+        ADD
+        | MUL
+        | DIV
+        | MOD
+        | AND
+        | OR
+        | XOR
+        | SHL
+        | SHR
+        | CMPEQ
+        | CMPLT
+        | JMP
+        | JZ
+        | JNZ
+        | LOAD
+        | REGCOPY
+        | MEMCOPY
+        | STORE => 4,
+        // Immediates - 4+ bytes
+        STOREIMM64 => 16,
+        STOREIMM32 => 8,
+        _ => panic!("unknown instruction op 0x{:04x}", op),
+    }
+}