Fixed bug with VM assigning wrong opcode

- Fixed a bug with VM assigning wrong opcode. After doing a little digging into the Iridium 1 source code (skipping to the next part of the tutorial), I discovered I had to have implement from() function in both directions. I.e. the Opcode outputs integer and integer outputs an Opcode. Derp moment in retrospective since I already had it done for the former but this is a learning experience.
- Moved Opcode enum to assembler module.

docs/README.md

@@ -1,6 +1,6 @@
 # Welcome
 
-Corten is a stack-based virtual machine written in Rust as a hobby. It's based on the [Iridium 1](spec.md#Iridium) architecture from Fletcher Haynes's [So you want to build a language VM](https://blog.subnetzero.io/post/building-language-vm-part-01/).
+Corten is a Corten [MIPS64 Release 6](https://en.wikipedia.org/wiki/MIPS_architecture#MIPS32/MIPS64_Release_6)  virtual machine written in Rust as a hobby based on Fletcher Haynes's [So you want to build a language VM](https://blog.subnetzero.io/post/building-language-vm-part-01/).
 
 ## Specifications
 

docs/spec.md

@@ -2,7 +2,7 @@
 
 ## Iridium
 
-Corten is based on Fletcher Haynes's [So you want to build a language VM](https://blog.subnetzero.io/post/building-language-vm-part-01/) tutorial. His virtual machine used for the tutorial is known as [Iridium](https://github.com/fhaynes/iridium) and is based on the [MIPS64 Release 6](https://en.wikipedia.org/wiki/MIPS_architecture#MIPS32/MIPS64_Release_6) architecture. Corten aims to be Iridium 1-compatible.
+Corten [MIPS64 Release 6](https://en.wikipedia.org/wiki/MIPS_architecture#MIPS32/MIPS64_Release_6) virtual machine based on Fletcher Haynes's [So you want to build a language VM](https://blog.subnetzero.io/post/building-language-vm-part-01/) tutorial.
 
 ## Instruction Set