Add Opcode struct (#2)

The Opcode must represent a full instruction for the VM and comply with
the specification:
https://github.com/FuelLabs/fuel-specs/blob/master/specs/vm/opcodes.md

[`std::io`] is used for serialization/deserialization targetting
compatibility.

Resolves #1

fuel-asm/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "fuel-asm"
+description = "Defines all opcodes available in the FuelVM."
+version = "0.1.0"
+authors = ["Victor Lopez <victor.lopez@fuel.sh>"]
+edition = "2018"
+repository = "https://github.com/FuelLabs/fuel-asm"
+license = "Apache-2.0"
+keywords = ["blockchain", "cryptocurrencies", "fuel-vm", "vm"]
+categories = ["cryptography::cryptocurrencies", "data-structures", "parsing"]
+
+[dependencies]

fuel-asm/rustfmt.toml

@@ -0,0 +1,2 @@
+max_width = 120
+wrap_comments = true

fuel-asm/src/lib.rs

@@ -0,0 +1,10 @@
+#![feature(arbitrary_enum_discriminant)]
+#![feature(external_doc)]
+#![warn(missing_docs)]
+#![doc(include = "../README.md")]
+
+mod opcode;
+mod types;
+
+pub use opcode::Opcode;
+pub use types::{Immediate06, Immediate12, Immediate18, Immediate24, RegisterId, Word};