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.cc

@@ -1,4 +1,35 @@
 #include "bus.hh"
+#include <memory>
 
-Bus::Bus(Memory&& memory)
-  : memory(std::move(memory)) {}
+Bus::Bus(std::shared_ptr<Memory> memory)
+  : memory(memory) {}
+
+uint8_t
+Bus::read_byte(size_t address) {
+    return memory->read(address);
+}
+
+void
+Bus::write_byte(size_t address, uint8_t byte) {
+    memory->write(address, byte);
+}
+
+uint16_t
+Bus::read_halfword(size_t address) {
+    return memory->read_halfword(address);
+}
+
+void
+Bus::write_halfword(size_t address, uint16_t halfword) {
+    memory->write_halfword(address, halfword);
+}
+
+uint32_t
+Bus::read_word(size_t address) {
+    return memory->read_word(address);
+}
+
+void
+Bus::write_word(size_t address, uint32_t word) {
+    memory->write_halfword(address, word);
+}