add a basic structure for disassembler + executor

Instructions added
Branch and Exchange (BX)
Branch and Link (B)
Multiply and Accumulate (MUL, MLA)
Multiply Long and Accumulate (SMULL, SMLAL, UMULL, UMLAL)
Single data swap (SWP)
[WIP] Halfword Transfer (STRH, LDRH)

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

src/bus.hh

@@ -1,11 +1,21 @@
 #pragma once
 
 #include "memory.hh"
+#include <memory>
 
 class Bus {
   public:
-    Bus(Memory&& memory);
+    Bus(std::shared_ptr<Memory> memory);
+
+    uint8_t read_byte(size_t address);
+    void write_byte(size_t address, uint8_t byte);
+
+    uint16_t read_halfword(size_t address);
+    void write_halfword(size_t address, uint16_t halfword);
+
+    uint32_t read_word(size_t address);
+    void write_word(size_t address, uint32_t word);
 
   private:
-    Memory memory;
+    std::shared_ptr<Memory> memory;
 };