docs update

docs/ISA REVISION notes.md

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+- we definitely need to be able to use registers for shift operations.
+- we need logical boolean operations in addition to the bitwise ones.
+- better conditionals.

docs/todo.md

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+# Compiler optimisations!
+
+- [ ] [HARD] Immediate operations for values that support it (up to +/- u16::max for addi and subi respectively) 
+  - this requires significant complexity in code generation as we need to traverse down the tree when we come across these operations to prevent additional register allocations.
+
+- [ ] [EASY] Add multiply and divide operations to code generation
+- [ ] [MEDIUM] proper prefix/postfix inc/dec implementation. slightly more complex as we need to check for a variable and modify it in place
+- [ ] [EASY] Investigate logical and operator not compiling - either a lexer or parser issue.
+- [x] [MEDIUM] Get shift operations working correctly.