Add lists

This introduces:

* new syntax for list literals, put comma-separated values between
  braces for your new list
* new syntax for indexing, do `foo[index]` to get the value in `foo` at
  `index`. Lists also allow negative indices too. Any type that wants to
  be indexed can include their own __index__ function as well.
* new VM instruction, BuildList. List literals were a lot easier to
  implement using this rather than creating a new list, creating a
  temporary stack value, and then duplicating + pushing to that
  temporary value over and over.

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

src/disassemble.rs

@@ -99,6 +99,11 @@ fn disassemble_chunk(chunk: &Chunk, constants: &Vec<ObjP>, globals: &Vec<String>
                 arg = format!("{depth}");
                 info = format!("slot {slot} (name unknown)");
             }
+            Op::BuildList(len) => {
+                op_str = "BUILD_LIST";
+                arg = format!("{len}");
+                info = String::new();
+            }
             Op::Nop => {
                 op_str = "NOP";
                 arg = String::new();